feat(desktop): Tier B web side — toast actions, Focus Assist gate, folder DnD

- P5-41/35 useTauriToastActions: native rich-toast click → navigate(path) (opens
  the room), quick reply → mx.sendMessage(roomId, m.text). The desktop bridge
  routes message notifications (tag=roomId) to show_rich_toast.
- P5-56 useTauriFocusAssist + focusAssistActiveAtom: a native focus-assist-changed
  event drives the atom, OR'd into the existing quiet-hours gate in
  ClientNonUIFeatures so notifications+sounds suppress during Windows Focus Assist.
- P5-48 recursive folder drag-drop: fileEntries.ts (sync webkitGetAsEntry capture
  → async batched readEntries traversal, path-prefixed names, 500-file cap) wired
  into useFileDrop, reusing the existing upload pipeline. +3 unit tests.

Hooks no-op in the browser. Gates: tsc/eslint/prettier clean, build OK, 559 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/components/TauriDesktopFeatures.tsx

@@ -3,6 +3,8 @@ import { useTauriJumpList } from '../hooks/useTauriJumpList';
 import { useTauriThumbbar } from '../hooks/useTauriThumbbar';
 import { useTauriSmtc } from '../hooks/useTauriSmtc';
 import { useTauriNetwork } from '../hooks/useTauriNetwork';
+import { useTauriToastActions } from '../hooks/useTauriToastActions';
+import { useTauriFocusAssist } from '../hooks/useTauriFocusAssist';
 
 /**
  * Mounts the client-scoped native desktop feature hooks (call/room aware). Each
@@ -17,5 +19,7 @@ export function TauriDesktopFeatures(): null {
   useTauriThumbbar(); // P5-44 taskbar thumbnail toolbar (mute/deafen/end)
   useTauriSmtc(); // P5-43 system media transport controls
   useTauriNetwork(); // P5-49 network-change awareness → sync retry
+  useTauriToastActions(); // P5-41/35 rich toast click → open room, quick reply → send
+  useTauriFocusAssist(); // P5-56 Windows Focus Assist → DND suppression atom
   return null;
 }