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-core/config/config.yaml.example

@@ -21,9 +21,9 @@ scheduler:
 
 dispatcher:
   poll_interval: 30           # 轮询间隔（秒）
-  edge_url: "http://100.x.x.20:5000/api/edge/video/analyze"
-  webhook_url: "http://100.x.x.10:8000/api/core/callback/event"
+  edge_url: "http://100.x.x.20:5000/api/edge/video/push"   # 推送模式端点（视频上传，同步返回结果）
   max_retries: 3
+  push_timeout: 1800          # 推送+分析同步超时（秒）
 
 video_server:
   base_url: "http://100.x.x.10:8000/media"