feat: 新增视频分析流水线、Web界面、孤儿清理工具；修复健壮性问题

- 新增 analysis/ 模块：MOG2活动检测、YOLO人物跟踪、MediaPipe摔倒检测、Ollama活动打标、缩略图抽取
- 新增 webapp/：Flask事件浏览界面，按需HEVC→H264转码缓存
- 新增 analyze.py：7阶段状态机流水线（scan→backfill→motion→person→fall→activity→thumbnail）
- 新增 cleanup_orphans.py：清理文件已删除的数据库孤儿记录
- 修复：motion/person/activity三阶段加单视频异常兜底，避免批次中断
- 修复：ollama_client加健康检查和3次重试，num_ctx从8192降到2048
- 修复：transcode_cache加fcntl文件锁，防止并发转码同一视频
- 修复：SQLite开WAL模式+busy_timeout，支持读写并发
- 修复：sync.py ffmpeg路径改为shutil.which查找，删除automate.py死代码PYTHON
- 修复：thumbnail失败加3次重试上限，避免无限重试损坏文件
- 新增：requirements.lock锁定版本、README文档
- 更新：.gitignore排除.playwright-mcp、截图、备份文件

webapp/static/style.css

@@ -0,0 +1,96 @@
+body {
+    font-family: -apple-system, "PingFang SC", sans-serif;
+    margin: 20px;
+    color: #222;
+}
+
+.filters {
+    margin-bottom: 16px;
+    display: flex;
+    gap: 16px;
+    align-items: center;
+}
+
+#stats {
+    color: #666;
+    font-size: 0.9em;
+}
+
+.cache-panel {
+    margin-bottom: 16px;
+    display: flex;
+    gap: 12px;
+    align-items: center;
+    color: #666;
+    font-size: 0.9em;
+}
+
+.cache-panel button {
+    cursor: pointer;
+}
+
+.main {
+    display: flex;
+    gap: 20px;
+}
+
+.player-panel {
+    flex: 1;
+}
+
+#player {
+    width: 100%;
+    max-width: 640px;
+    background: #000;
+}
+
+#player-info {
+    margin-top: 8px;
+    color: #555;
+    font-size: 0.9em;
+}
+
+.event-list {
+    flex: 1;
+    max-height: 80vh;
+    overflow-y: auto;
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+}
+
+.event-item {
+    display: flex;
+    gap: 10px;
+    cursor: pointer;
+    padding: 6px;
+    border-radius: 6px;
+}
+
+.event-item:hover {
+    background: #f0f0f0;
+}
+
+.event-thumb {
+    width: 120px;
+    height: 68px;
+    object-fit: cover;
+    background: #ddd;
+    border-radius: 4px;
+    flex-shrink: 0;
+}
+
+.event-info {
+    display: flex;
+    flex-direction: column;
+    justify-content: center;
+}
+
+.event-type {
+    font-weight: 600;
+}
+
+.event-time {
+    color: #666;
+    font-size: 0.9em;
+}