feat(v1): settings camera connection test and preview

Settings tab gains a camera group (host/port/channel/user/masked password),
a background connection-test worker that probes one frame off the GUI
thread and shows it in a preview, and a save button that writes the
structured source to the untracked config.local.json. 60 tests pass;
Qt shell compiles and needs a Windows smoke.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/04-architecture.md

@@ -32,6 +32,7 @@ V1 的同一数据流既可接 RTSP，也可回放本地录像。V2 复用同一
 | --- | --- | --- | --- |
 | 应用入口 | `v1/app.py` | 装配配置、窗口、线程和依赖 | 推理细节、事件判定 |
 | 配置 | `v1/config.py` | 解析示例和本地配置，校验非敏感字段 | 保存真实凭证 |
+| 摄像头接入 | `v1/camera.py` | 由 host/port/channel/账号/密码构建 RTSP URL（凭证百分号编码），并对流做一次有界连接测试抓帧 | 事件判定、持久化 |
 | 视频源 | `v1/video_source.py` | 打开、读取、重连 RTSP 或录像；输出帧、单调回放时间戳和显式来源状态 | Pose、报警 |
 | Pose 适配器 | `v1/pose.py` | 校验锁定模型的 SHA-256、pose/person/17×3 契约，统一返回 box、关键点、置信度 | 跟踪、摔倒业务结论 |
 | 跟踪 | `v1/tracking.py` | 以归一化 box 中心距离为连续人员输出稳定 `track_id` | 根据姿态报警 |