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.

src/screens/home/PostDetailScreen.tsx

@@ -1084,6 +1084,12 @@ export const PostDetailScreen: React.FC = () => {
     }));
   }, [post?.images]);
 
+  // 为 ImageGallery 提供稳定的图片列表，避免 Math.random() 在每次渲染时生成新 ID
+  const stableGalleryImages = useMemo(() => allImages.map((img, i) => ({
+    id: img.id || img.url || `img-${i}`,
+    url: img.url || img.uri || ''
+  })), [allImages]);
+
   // 渲染帖子头部 - 小红书/微博风格
   const renderPostHeader = useCallback(() => {
     if (!post) return null;
@@ -1740,10 +1746,7 @@ export const PostDetailScreen: React.FC = () => {
         {/* 图片预览 ImageGallery */}
         <ImageGallery
           visible={showImageModal}
-          images={allImages.map(img => ({ 
-            id: img.id || img.url || String(Math.random()), 
-            url: img.url || img.uri || '' 
-          }))}
+          images={stableGalleryImages}
           initialIndex={selectedImageIndex}
           onClose={() => setShowImageModal(false)}
           enableSave
@@ -1815,10 +1818,7 @@ export const PostDetailScreen: React.FC = () => {
       {/* 图片预览 ImageGallery */}
       <ImageGallery
         visible={showImageModal}
-        images={allImages.map(img => ({ 
-          id: img.id || img.url || String(Math.random()), 
-          url: img.url || img.uri || '' 
-        }))}
+        images={stableGalleryImages}
         initialIndex={selectedImageIndex}
         onClose={() => setShowImageModal(false)}
         enableSave