feat(monitoring): decouple AI platforms from media_platforms and expand catalog to 6

Add ai_platforms table + shared catalog (yuanbao/kimi/wenxin/deepseek/doubao/qwen),
drop FKs from platform_accounts and desktop_tasks to media_platforms, and wire
target_account_id + platform into DesktopTaskEvent so the desktop runtime no
longer has to infer them from local state. Desktop client gains generic AI page
detection for binding, drops stale-business-date monitor tasks at the edge, and
refactors AccountsView/AiPlatformsView around the shared catalog. Admin tracking
view surfaces per-platform sampling status cards.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop-client/package.json

@@ -22,6 +22,7 @@
     "electron-updater": "^6.0.0",
     "marked": "^17.0.5",
     "pino": "^9.0.0",
+    "playwright-core": "^1.55.0",
     "vue": "^3.5.31",
     "vue-router": "^4.5.1"
   },