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>

pnpm-lock.yaml

@@ -156,6 +156,9 @@ importers:
       pino:
         specifier: ^9.0.0
         version: 9.7.0
+      playwright-core:
+        specifier: ^1.55.0
+        version: 1.59.1
       vue:
         specifier: ^3.5.31
         version: 3.5.31(typescript@5.9.3)