fix(chart): 纵轴自 0 起、刻度归位、数据点恢复为正圆

- 纵轴从 0 起，上界取整到好读的数（1/1.2/1.5/2/…）。此前按 [最小值,最大值] 自适应，491→506 这点变化被撑满整个图高、看着像暴涨，且上下两刻度就是 506 和 491 两个几乎一样的数，没有 0 做参照读不出量级
- 刻度线画在 0 / 中值 / 上界，标签贴在各自主线上、放进左侧刻度栏。原来是两个绝对定位的数字浮在图面上，会挤在一起读成一个数
- 数据点恢复为正圆：根因是 preserveAspectRatio="none" 把 600×160 的 viewBox 横向拉满容器，横纵缩放不一致，半径 4 的圆被压成椭圆。改为用 ResizeObserver 量出容器宽度、等比绘图
- 每个数据点都画出来（原先只画末点），点数多时自动缩小半径；悬停热区按点位间距铺满整段，不再固定 12px
- 当前值移到标题行，不再浮在图面上遮挡曲线

webui/src/components/monitor/NoteTrendChart.tsx

@@ -1,4 +1,4 @@
-import { useMemo, useState } from 'react'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 
 import { useNoteSeries } from '@/hooks/useMonitor'
 import { formatCount, formatDateTime } from '@/lib/monitorFormat'
@@ -12,13 +12,29 @@ const METRICS: Array<{ key: MetricKey; label: string }> = [
   { key: 'share_count', label: '分享' },
 ]
 
-const VIEW_W = 600
+/** 图表高度固定；宽度由容器量出来，见下方 attachContainer。 */
 const VIEW_H = 160
-const PAD_LEFT = 10
-const PAD_RIGHT = 56
-const PAD_TOP = 18
+const PAD_LEFT = 44 // 左侧刻度栏，要放得下 "1.2万"
+const PAD_RIGHT = 16
+const PAD_TOP = 14
 const PAD_BOTTOM = 22
 
+/**
+ * 把纵轴上界向上取到一个好读的数（1 / 1.2 / 1.5 / 2 / …）。
+ *
+ * 纵轴刻意从 0 起。原先按 [最小值, 最大值] 自适应，于是 491 -> 506 这点变化被撑满
+ * 整个图高、看着像暴涨；而且上下两个刻度就是 "506" 和 "491" 两个几乎一样的数，
+ * 没有 0 做参照，根本读不出量级。
+ */
+const NICE_STEPS = [1, 1.2, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10]
+
+function niceMax(value: number): number {
+  if (value <= 0) return 1
+  const magnitude = 10 ** Math.floor(Math.log10(value))
+  const step = NICE_STEPS.find((candidate) => value / magnitude <= candidate) ?? 10
+  return step * magnitude
+}
+
 interface NoteTrendChartProps {
   noteId: string
   taskId: number | null
@@ -36,8 +52,25 @@ interface NoteTrendChartProps {
 export function NoteTrendChart({ noteId, taskId, noteTitle }: NoteTrendChartProps) {
   const [metric, setMetric] = useState<MetricKey>('liked_count')
   const [hoverIndex, setHoverIndex] = useState<number | null>(null)
+  const [width, setWidth] = useState(0)
+  const observer = useRef<ResizeObserver | null>(null)
   const { data: series, isLoading } = useNoteSeries(noteId, taskId)
 
+  // 宽度是量出来的，不是拉伸出来的。原先靠 preserveAspectRatio="none" 把 600×160 的
+  // viewBox 横向撑满容器 —— 横纵缩放不一致，半径 4 的圆就被压成了椭圆。只有等比绘图，
+  // 圆才真的是圆。
+  const attachContainer = useCallback((node: HTMLDivElement | null) => {
+    observer.current?.disconnect()
+    if (!node) return
+    const measure = () => setWidth(Math.round(node.getBoundingClientRect().width))
+    const resizeObserver = new ResizeObserver(measure)
+    resizeObserver.observe(node)
+    observer.current = resizeObserver
+    measure()
+  }, [])
+
+  useEffect(() => () => observer.current?.disconnect(), [])
+
   // A point with no parsed value is a gap, not a zero.
   const points = useMemo(
     () => (series ?? []).filter((point) => point[metric] !== null),
@@ -45,40 +78,57 @@ export function NoteTrendChart({ noteId, taskId, noteTitle }: NoteTrendChartProp
   )
 
   const geometry = useMemo(() => {
-    if (points.length < 2) return null
+    if (points.length < 2 || width <= 0) return null
 
     const values = points.map((point) => point[metric] as number)
-    const min = Math.min(...values)
-    const max = Math.max(...values)
-    // A flat series would divide by zero; give it a nominal band.
-    const span = max - min || 1
+    const axisMax = niceMax(Math.max(...values))
 
-    const innerW = VIEW_W - PAD_LEFT - PAD_RIGHT
+    const innerW = Math.max(1, width - PAD_LEFT - PAD_RIGHT)
     const innerH = VIEW_H - PAD_TOP - PAD_BOTTOM
 
     const xy = points.map((point, index) => {
       const value = point[metric] as number
       return {
         x: PAD_LEFT + (index / (points.length - 1)) * innerW,
-        y: PAD_TOP + innerH - ((value - min) / span) * innerH,
+        y: PAD_TOP + innerH - (value / axisMax) * innerH,
         value,
         point,
       }
     })
 
-    return { xy, min, max }
-  }, [points, metric])
+    return { xy, axisMax, innerW, innerH }
+  }, [points, metric, width])
 
   if (isLoading) {
     return <div className="p-4 text-[11px] font-mono text-cyber-text-muted">加载中…</div>
   }
 
+  const metricLabel = METRICS.find((option) => option.key === metric)?.label ?? ''
+  const latest = points.length > 0 ? (points[points.length - 1][metric] as number) : null
+
+  // Fewer points get a bigger dot; a dense series would otherwise turn into a
+  // string of overlapping beads.
+  const dotRadius = points.length > 12 ? 2.5 : 4
+  const hitWidth = geometry ? Math.max(12, geometry.innerW / Math.max(1, points.length - 1)) : 12
+
   return (
     <div className="space-y-2">
       <div className="flex items-center justify-between gap-3 flex-wrap">
-        <span className="font-mono text-xs text-cyber-text-primary">
-          指标趋势 · <span className="text-cyber-text-secondary">{noteTitle || noteId}</span>
-        </span>
+        <div className="flex items-baseline gap-2 min-w-0">
+          <span className="font-mono text-xs text-cyber-text-primary flex-shrink-0">指标趋势</span>
+          <span
+            className="font-mono text-[11px] text-cyber-text-secondary truncate"
+            title={noteTitle || noteId}
+          >
+            {noteTitle || noteId}
+          </span>
+          {latest !== null && (
+            <span className="font-mono text-xs text-cyber-neon-cyan flex-shrink-0">
+              {formatCount(latest)}
+              <span className="text-cyber-text-muted text-[10px] ml-1">{metricLabel}</span>
+            </span>
+          )}
+        </div>
         <div className="flex items-center gap-1">
           {METRICS.map((option) => (
             <button
@@ -96,97 +146,101 @@ export function NoteTrendChart({ noteId, taskId, noteTitle }: NoteTrendChartProp
         </div>
       </div>
 
-      {!geometry ? (
+      {points.length < 2 ? (
         <p className="py-6 text-center text-[11px] font-mono text-cyber-text-muted">
           至少需要两轮采集才能画出趋势（当前 {points.length} 个有效数据点）
         </p>
       ) : (
-        <div className="relative">
-          <svg
-            viewBox={`0 0 ${VIEW_W} ${VIEW_H}`}
-            className="w-full h-40"
-            preserveAspectRatio="none"
-            onMouseLeave={() => setHoverIndex(null)}
-          >
-            {/* Recessive solid hairlines - never dashed. */}
-            {[0, 0.5, 1].map((ratio) => {
-              const y = PAD_TOP + (VIEW_H - PAD_TOP - PAD_BOTTOM) * ratio
-              return (
+        <div className="relative" ref={attachContainer}>
+          {geometry && (
+            <svg
+              width={width}
+              height={VIEW_H}
+              viewBox={`0 0 ${width} ${VIEW_H}`}
+              className="block"
+              onMouseLeave={() => setHoverIndex(null)}
+            >
+              {/* 刻度线画在 0 / 中值 / 上界上，标签就贴在对应位置 —— 不再浮在图面上，
+                  也就不会出现两个数挤在一起读成一个数的情况。 */}
+              {[0, 0.5, 1].map((ratio) => {
+                const y = PAD_TOP + geometry.innerH * ratio
+                return (
+                  <g key={ratio}>
+                    <line
+                      x1={PAD_LEFT}
+                      x2={width - PAD_RIGHT}
+                      y1={y}
+                      y2={y}
+                      stroke="rgb(var(--cyber-text-muted) / 0.25)"
+                      strokeWidth={1}
+                    />
+                    <text
+                      x={PAD_LEFT - 8}
+                      y={y}
+                      textAnchor="end"
+                      dominantBaseline="middle"
+                      fontSize={9}
+                      fill="rgb(var(--cyber-text-muted))"
+                      style={{ fontFamily: 'ui-monospace, SFMono-Regular, monospace' }}
+                    >
+                      {formatCount(Math.round(geometry.axisMax * (1 - ratio)))}
+                    </text>
+                  </g>
+                )
+              })}
+
+              {hoverIndex !== null && geometry.xy[hoverIndex] && (
                 <line
-                  key={ratio}
-                  x1={PAD_LEFT}
-                  x2={VIEW_W - PAD_RIGHT}
-                  y1={y}
-                  y2={y}
-                  stroke="rgb(var(--cyber-text-muted) / 0.25)"
+                  x1={geometry.xy[hoverIndex].x}
+                  x2={geometry.xy[hoverIndex].x}
+                  y1={PAD_TOP}
+                  y2={PAD_TOP + geometry.innerH}
+                  stroke="rgb(var(--cyber-neon-cyan) / 0.5)"
                   strokeWidth={1}
-                  vectorEffect="non-scaling-stroke"
                 />
-              )
-            })}
+              )}
 
-            {hoverIndex !== null && geometry.xy[hoverIndex] && (
-              <line
-                x1={geometry.xy[hoverIndex].x}
-                x2={geometry.xy[hoverIndex].x}
-                y1={PAD_TOP}
-                y2={VIEW_H - PAD_BOTTOM}
-                stroke="rgb(var(--cyber-neon-cyan) / 0.5)"
-                strokeWidth={1}
-                vectorEffect="non-scaling-stroke"
+              <polyline
+                points={geometry.xy.map((node) => `${node.x},${node.y}`).join(' ')}
+                fill="none"
+                stroke="rgb(var(--cyber-neon-cyan))"
+                strokeWidth={2}
+                strokeLinejoin="round"
+                strokeLinecap="round"
               />
-            )}
 
-            <polyline
-              points={geometry.xy.map((node) => `${node.x},${node.y}`).join(' ')}
-              fill="none"
-              stroke="rgb(var(--cyber-neon-cyan))"
-              strokeWidth={2}
-              strokeLinejoin="round"
-              strokeLinecap="round"
-              vectorEffect="non-scaling-stroke"
-            />
+              {geometry.xy.map((node, index) => (
+                <circle
+                  key={index}
+                  cx={node.x}
+                  cy={node.y}
+                  r={dotRadius}
+                  fill="rgb(var(--cyber-neon-cyan))"
+                  // 与环境色同色的描边，让重叠的点之间留出间隙。
+                  stroke="rgb(var(--cyber-bg-primary))"
+                  strokeWidth={2}
+                />
+              ))}
 
-            {/* Only the endpoint is labelled - a number on every point is noise. */}
-            <circle
-              cx={geometry.xy[geometry.xy.length - 1].x}
-              cy={geometry.xy[geometry.xy.length - 1].y}
-              r={4}
-              fill="rgb(var(--cyber-neon-cyan))"
-              stroke="rgb(var(--cyber-bg-primary))"
-              strokeWidth={2}
-              vectorEffect="non-scaling-stroke"
-            />
+              {geometry.xy.map((node, index) => (
+                <rect
+                  key={index}
+                  x={node.x - hitWidth / 2}
+                  y={PAD_TOP}
+                  width={hitWidth}
+                  height={geometry.innerH}
+                  fill="transparent"
+                  onMouseEnter={() => setHoverIndex(index)}
+                />
+              ))}
+            </svg>
+          )}
 
-            {geometry.xy.map((node, index) => (
-              <rect
-                key={index}
-                x={node.x - 6}
-                y={PAD_TOP}
-                width={12}
-                height={VIEW_H - PAD_TOP - PAD_BOTTOM}
-                fill="transparent"
-                onMouseEnter={() => setHoverIndex(index)}
-              />
-            ))}
-          </svg>
-
-          {/* Axis extremes live in text tokens, never the series colour. */}
-          <span className="absolute left-0 top-0 text-[9px] font-mono text-cyber-text-muted">
-            {formatCount(geometry.max)}
-          </span>
-          <span className="absolute left-0 bottom-5 text-[9px] font-mono text-cyber-text-muted">
-            {formatCount(geometry.min)}
-          </span>
-          <span className="absolute right-0 top-1/2 -translate-y-1/2 text-[11px] font-mono text-cyber-text-primary">
-            {formatCount(geometry.xy[geometry.xy.length - 1].value)}
-          </span>
-
-          {hoverIndex !== null && geometry.xy[hoverIndex] && (
+          {hoverIndex !== null && geometry?.xy[hoverIndex] && (
             <div
-              className="absolute -top-1 px-2 py-1 rounded border border-cyber-border-DEFAULT bg-cyber-bg-elevated text-[10px] font-mono text-cyber-text-primary pointer-events-none whitespace-nowrap"
+              className="absolute -top-1 px-2 py-1 rounded border border-cyber-border-DEFAULT bg-cyber-bg-elevated text-[10px] font-mono text-cyber-text-primary pointer-events-none whitespace-nowrap z-10"
               style={{
-                left: `${(geometry.xy[hoverIndex].x / VIEW_W) * 100}%`,
+                left: `${(geometry.xy[hoverIndex].x / width) * 100}%`,
                 transform: 'translateX(-50%)',
               }}
             >
@@ -202,7 +256,7 @@ export function NoteTrendChart({ noteId, taskId, noteTitle }: NoteTrendChartProp
       )}
 
       <p className="text-[10px] font-mono text-cyber-text-muted">
-        共 {points.length} 个数据点，每轮采集记录一次快照
+        共 {points.length} 个数据点，每轮采集记录一次快照 · 纵轴自 0 起
       </p>
     </div>
   )