feat: CDP 接管开关 + 扫码登录面板 + Docker 部署

- runner: enable_cdp_mode 从硬编码 False 改为系统设置 cdp_enabled。服务器部署下爬虫接管已开启远程调试的 Chrome（默认 9222），复用其 profile 登录态；本机桌面默认仍为关，行为不变
- qrlogin: 新增 CDP 扫码登录。Chrome 在服务器上跑于 Xvfb，show_qrcode 依赖的 PIL 桌面看图程序不存在，二维码无处可显示；改为经 CDP 从页面取出二维码交给 WebUI 渲染。刻意复用 browser.contexts[0]（新建 context 是无痕 profile，扫了也白扫），且绝不调用 browser.close()（会连带关掉操作者自己的 Chrome）
- webui: 设置页新增扫码面板，替换原本跳到采集页看终端二维码的入口
- Dockerfile / .dockerignore / docker-compose.yml: 服务器部署。host 网络是必需而非图省事——容器里 127.0.0.1:9222 必须落到宿主机回环
- UPSTREAM.md: 补充 gitcode 镜像，用于 GitHub 大包传输必断时补历史

docker-compose.yml

@@ -0,0 +1,24 @@
+services:
+  mediacrawler:
+    build: .
+    image: mediacrawler:latest
+    container_name: mediacrawler
+    restart: unless-stopped
+
+    # host networking is a requirement, not a convenience: the crawler attaches
+    # to the operator's Chrome at 127.0.0.1:9222, and inside a bridge network
+    # that loopback is the container's own, where no browser is listening.
+    # It also puts the app port directly on the host, so `ports:` is not used.
+    network_mode: host
+
+    env_file:
+      - .env
+    environment:
+      MC_HOST: 0.0.0.0
+      MC_PORT: "18051"
+      TZ: Asia/Shanghai
+
+    volumes:
+      # Per-run crawler output, read back by the monitor layer. Without this the
+      # data would live inside the container and vanish on every rebuild.
+      - ./data:/app/data