feat(p1): add daily snapshots and fan tracking

Implement P1: seven-metric view snapshots, relation/stat fan snapshots, failure placeholders, resume by daily completion markers, Cookie login warnings, daily SQLite backups, Shanghai daily scheduling, and CLI snapshot/auth-check commands. Real read-only run captured 795/795 videos successfully over 1124s with a verified daily backup.

app.py

@@ -1,8 +1,8 @@
 # -*- coding: utf-8 -*-
 """看板服务入口。
 
-P0 提供 ``init`` / ``sync`` / ``run`` / ``status`` 子命令；后续阶段会在同一入口启动
-本地 Web 服务。
+P1 提供 ``init`` / ``sync`` / ``snapshot`` / ``auth-check`` / ``run`` / ``status``
+子命令；后续阶段会在同一入口启动本地 Web 服务。
 """
 
 import sys