perf(stores): defer safeStorage writes off the interaction path (#1941)

* perf(stores): defer safeStorage writes off the interaction path

Session switches funnel every persisted store slice through safeStorage.setItem,
and doing those large JSON.stringify writes synchronously blocked the main
thread for over a second. Add a write-behind buffer that:

- Defers each setItem/removeItem to a later task via setTimeout(0) so the
  click-to-paint path is not blocked.
- Coalesces repeated writes to the same key into a single backing flush.
- Serves pending values from memory so read-after-write stays consistent
  within the deferral window.
- Flushes synchronously on pagehide/beforeunload/visibilitychange/freeze so
  deferred state survives tab close, reload, and the mobile freeze lifecycle.

Adds a test covering write deferral, coalescing, and pending read serving.

* fix(stores): defer persisted JSON serialization

* fix(stores): defer direct safeStorage writes

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/stores/useDirectoryStore.ts

@@ -6,7 +6,7 @@ import { subscribeRuntimeEndpointChanged } from '@/lib/runtime-switch';
 import { updateDesktopSettings } from '@/lib/persistence';
 import { useFileSearchStore } from '@/stores/useFileSearchStore';
 import { streamDebugEnabled } from '@/stores/utils/streamDebug';
-import { getSafeStorage } from './utils/safeStorage';
+import { getDeferredSafeStorage } from './utils/safeStorage';
 
 interface DirectoryStore {
 
@@ -28,7 +28,7 @@ interface DirectoryStore {
 
 let cachedHomeDirectory: string | null = null;
 let homeResolveGeneration = 0;
-const safeStorage = getSafeStorage();
+const safeStorage = getDeferredSafeStorage();
 const persistedLastDirectory = safeStorage.getItem('lastDirectory');
 const initialHasPersistedDirectory =
   typeof persistedLastDirectory === 'string' && persistedLastDirectory.length > 0;