refactor(core): optimize state management and component rendering performance

Improve application stability and performance by optimizing Zustand store usage, implementing memoization patterns, and introducing persistent authentication.

- **State Management**:
  - Refactor Zustand selectors to use `useShallow` and `getState()` to prevent unnecessary re-renders and infinite loops in hooks.
  - Implement `persist` middleware for `authStore` to maintain user sessions across restarts.
  - Introduce `buildStateCached` in `themeStore` to reduce redundant theme object computations.
- **Performance & Rendering**:
  - Implement `useMemo` for stable object/array references in `ImageGallery` and list components to prevent expensive re-renders.
  - Replace inline arrow functions with `useCallback` in complex screens like `ChatScreen` and `MessageListScreen`.
  - Optimize `FlashList` usage by providing stable `key` and `extraData` props.
- **Architecture**:
  - Decouple unread count fetching by introducing `useUnreadCountQuery` (React Query) for better caching and synchronization.
  - Add `useChannels` hook to centralize channel data fetching.
  - Refine `SessionGate` logic to allow immediate rendering of authenticated users while verifying in the background.

app/_layout.tsx

@@ -101,15 +101,18 @@ function SystemChrome() {
 }
 
 function SessionGate({ children }: { children: React.ReactNode }) {
-  const [ready, setReady] = useState(false);
+  const isAuthenticated = useAuthStore((s) => s.isAuthenticated);
   const fetchCurrentUser = useAuthStore((s) => s.fetchCurrentUser);
   const colors = useAppColors();
+  const [verified, setVerified] = useState(false);
 
   useEffect(() => {
-    fetchCurrentUser().finally(() => setReady(true));
+    fetchCurrentUser().finally(() => setVerified(true));
   }, [fetchCurrentUser]);
 
-  if (!ready) {
+  // If persisted state shows authenticated, render immediately (background verify)
+  // If not authenticated and not yet verified, show loading
+  if (!isAuthenticated && !verified) {
     return (
       <View
         style={{
@@ -123,6 +126,7 @@ function SessionGate({ children }: { children: React.ReactNode }) {
       </View>
     );
   }
+  // If verified and not authenticated, the Redirect in (app)/_layout.tsx handles it
   return <>{children}</>;
 }