fix(dictation): abort in-flight start on cleanup/unmount

cleanup() tore down resources but never set startAbortedRef, so a
composer unmounting while startRecording() awaited start_dictation /
listen / getUserMedia / addModule would resume the async start against a
torn-down instance — opening the mic/worklet and leaving the native
session and event listeners running after the component was gone. Set
the abort flag first in cleanup(); a fresh startRecording clears it
before its first await, so subsequent starts are unaffected.

desktop/src/features/dictation/hooks/useLocalDictation.ts

@@ -197,6 +197,15 @@ export function useLocalDictation({
   }, []);
 
   const cleanup = useCallback(() => {
+    // Abort any in-flight startRecording so it bails after its next await
+    // instead of resuming and opening the mic/worklet or leaving the native
+    // session/listeners running after teardown. `cleanup` is the unmount
+    // handler (and the catch-path teardown); without this, unmounting while
+    // startRecording awaits `start_dictation`/`listen`/`getUserMedia`/
+    // `addModule` would let the async start finish against a torn-down
+    // instance. A fresh startRecording clears this flag before its first
+    // await, so it never wrongly aborts a subsequent start.
+    startAbortedRef.current = true;
     // Flush any remaining audio before teardown, then stop the native engine.
     // Scope the stop to THIS hook instance's session. `cleanup` runs as every
     // instance's unmount handler, so an unscoped stop here would let a