Move diff panel into thread route and lift worker pool provider

- Extract `DiffWorkerPoolProvider` into its own component and wrap `_chat` outlet with it
- Render/lazy-load `DiffPanel` from `/_chat/$threadId` so diff UI state and close behavior live with thread routing
- Keep responsive sheet vs inline diff presentation with route-level fallback loading UI
891eb02d49Julius Marminge committed on 2/19/2026, 5:49:50 PMparentcc3e1db
4 files changedLine totals unavailable