feat(ui): improve navigation, component props, and chat logic

- update `app.json` with splash screen configuration
- implement tab navigation redirection in `TabsLayout` for apps and profile tabs
- update `HighlightText` prop usage from `style` to `highlightStyle` in `PostCard` and `PostContentRenderer`
- fix chat message segment construction to avoid empty text segments when sending only images
- refine UI styling by removing unnecessary shadows and adjusting `UserScreen` header visibility
- improve `HomeScreen` scroll behavior by disabling animation on FlashList scroll-to-top

src/screens/home/HomeScreen.tsx

@@ -364,7 +364,7 @@ export const HomeScreen: React.FC = () => {
   useEffect(() => {
     if (homeTabPressCount > 0) {
       // 滚动 FlashList 到顶部
-      flashListRef.current?.scrollToOffset({ offset: 0, animated: true });
+      flashListRef.current?.scrollToOffset({ offset: 0, animated: false });
       // 滚动 ScrollView 到顶部（网格模式）
       scrollViewRef.current?.scrollTo({ y: 0, animated: true });
       // 重置底部 Tab 栏状态