feat: video analysis switched to push mode (upload whole video, sync response)

Rationale: Oracle cannot reach NAS (Tailscale userspace mode on NAS, no TUN),
the old pull+webhook design requires Edge to download video from NAS and
callback to NAS - both blocked. New design is one-way NAS -> Oracle:

- FAM-Edge: new POST /api/edge/video/push endpoint accepts multipart video
  upload, reuses existing OpenCV scene-change keyframe selection, analyzes
  synchronously and returns the result payload directly in the HTTP response
  (no webhook callback). Old /api/edge/video/analyze kept for compatibility.
- FAM-Edge: VideoPreprocessor.save_upload() saves the uploaded file
- FAM-Edge: AIOrchestrator.process_push_task() runs the full pipeline
  (health check -> extract -> select -> compress -> VLM -> fusion) and
  returns callback-style payload dict
- FAM-Core: Dispatcher rewritten to push mode - reads local video file,
  uploads with task metadata (camera_name, event_start_time from file mtime,
  known_members_context), applies the result to DB via shared
  event_receiver.apply_success_event()
- FAM-Core: event_receiver success logic extracted into reusable
  apply_success_event() (used by both webhook route and dispatcher)
- config: edge_url -> /api/edge/video/push, push_timeout 1800s, gunicorn
  Edge timeout raised to 1800s for long synchronous analysis

fam-edge/src/fam_edge/video_preprocessor/preprocessor.py

@@ -68,6 +68,17 @@ class VideoPreprocessor:
         log_task(logger, self.task_id, 'download', f'下载完成: {size_mb:.1f}MB', duration_ms=duration_ms)
         return self.video_path
 
+    def save_upload(self, file_storage) -> str:
+        """保存推送模式上传的视频文件（multipart），替代 download_video"""
+        os.makedirs(self.work_dir, exist_ok=True)
+        start = time.time()
+        file_storage.save(self.video_path)
+        duration_ms = int((time.time() - start) * 1000)
+        size_mb = os.path.getsize(self.video_path) / (1024 * 1024)
+        log_task(logger, self.task_id, 'upload',
+                 f'保存上传视频: {size_mb:.1f}MB', duration_ms=duration_ms)
+        return self.video_path
+
     def _get_video_duration(self, video_path: str) -> float:
         """用 ffprobe 获取视频时长（秒）"""
         try: