fix(desktop): hydrate Focus Assist on mount; thread-aware toast quick reply

- useTauriFocusAssist queries the new `get_focus_assist` command on mount.
  The native poll's first reading is emitted during app setup, before the
  page listens, and the atom resets on every reload — so with Focus Assist
  already on, notifications leaked until the OS state flipped
  (cinny-desktop #15).
- The toast quick reply takes the real `threadId` from the notification
  data and replies inside the thread (cinny-desktop #17).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useTauriFocusAssist.ts

@@ -1,6 +1,7 @@
+import { useEffect } from 'react';
 import { useSetAtom } from 'jotai';
 import { focusAssistActiveAtom } from '../state/focusAssist';
-import { useTauriEvent } from './useTauri';
+import { tauriInvoke, useTauriEvent } from './useTauri';
 
 /** Detail shape of the `focus-assist-changed` event emitted by the native side. */
 type FocusAssistChangedDetail = {
@@ -21,4 +22,16 @@ export function useTauriFocusAssist(): void {
   useTauriEvent<FocusAssistChangedDetail>('focus-assist-changed', ({ active }) =>
     setFocusAssist(active),
   );
+
+  // Hydrate on mount. The native poll only emits on a transition, and its first
+  // reading lands during app setup before this page is listening — so with Focus
+  // Assist already on at launch (or after a reload) notifications leaked until
+  // the OS state next flipped (cinny-desktop #15). `null` = no reading yet.
+  useEffect(() => {
+    tauriInvoke()?.('get_focus_assist')
+      .then((active) => {
+        if (typeof active === 'boolean') setFocusAssist(active);
+      })
+      .catch(() => undefined);
+  }, [setFocusAssist]);
 }