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/useConfigStore.test.ts

@@ -129,7 +129,23 @@ const deferred = <T,>() => {
 };
 
 mock.module('@/stores/utils/safeStorage', () => ({
+  getDeferredSafeStorage: () => makeStorage(),
   getSafeStorage: () => makeStorage(),
+  createDeferredSafeJSONStorage: () => {
+    const testStorage = makeStorage();
+    return {
+      getItem: (name: string) => {
+        const value = testStorage.getItem(name);
+        return value === null ? null : JSON.parse(value);
+      },
+      setItem: (name: string, value: unknown) => {
+        testStorage.setItem(name, JSON.stringify(value));
+      },
+      removeItem: (name: string) => {
+        testStorage.removeItem(name);
+      },
+    };
+  },
 }));
 
 mock.module('@/stores/useProjectsStore', () => ({