feat(p3): add discovery, telegram notifications, and one-click favorites

Implement WBI video search with legacy fallback, classification scoring, candidate pool, permanent seen-aid dedupe, blacklist filtering, and batched Telegram notifications. Add write client for fav deal/sort, target-folder selection, insertion position calculation, read-back verification, fav_action locking, retry on failure, ignore and blacklist actions. Wire discovery, candidate cleanup, Telegram long polling, and new discover/candidates CLI commands into the scheduler. Add migration v3 for candidate duration and index stats.

app.py

@@ -1,8 +1,9 @@
 # -*- coding: utf-8 -*-
 """看板服务入口。
 
-P1 提供 ``init`` / ``sync`` / ``snapshot`` / ``auth`` / ``auth-check`` / ``run`` / ``status``
-子命令；后续阶段会在同一入口启动本地 Web 服务。
+P1/P3 提供 ``init`` / ``sync`` / ``snapshot`` / ``discover`` / ``candidates`` /
+``auth`` / ``auth-check`` / ``run`` / ``status`` 子命令；P2 起在同一入口启动本地
+Web 服务。
 """
 
 import sys