feat(ui): implement keyword highlighting and improve search experience

- Add keyword highlighting in `PostCard` and `PostContentRenderer` using `HighlightText`.
- Implement smart excerpt logic in `PostCard` to show relevant context around search keywords.
- Update `SearchBar` styles for better visual feedback and consistency.
- Enhance `SearchScreen` with modern tab variants and improved tag styling.
- Add support for updating group descriptions in `GroupInfoScreen` and `GroupService`.
- Refactor various UI components for improved layout stability and typography.

src/screens/home/SearchScreen.tsx

@@ -265,7 +265,7 @@ export const SearchScreen: React.FC<SearchScreenProps> = ({ onBack }) => {
                 post={post}
                 onAction={(action) => handlePostAction(post, action)}
                 variant="list"
-                features={isMobile ? 'compact' : 'full'}
+                features="full"
                 highlightKeyword={currentKeyword}
               />
             ))}
@@ -288,7 +288,7 @@ export const SearchScreen: React.FC<SearchScreenProps> = ({ onBack }) => {
             post={item}
             onAction={(action) => handlePostAction(item, action)}
             variant="list"
-            features="compact"
+            features="full"
             highlightKeyword={currentKeyword}
           />
         )}
@@ -542,11 +542,12 @@ export const SearchScreen: React.FC<SearchScreenProps> = ({ onBack }) => {
           activeIndex={activeIndex}
           onTabChange={(index) => {
             setActiveIndex(index);
-            // 如果已经搜索过，切换Tab时重新搜索
             if (currentKeyword && hasSearched) {
               performSearch(currentKeyword);
             }
           }}
+          variant="modern"
+          icons={['file-document-outline', 'account-outline']}
         />
       </View>
 
@@ -571,22 +572,12 @@ function createSearchScreenStyles(colors: AppColors) {
     },
     searchShell: {
       flex: 1,
-      borderRadius: borderRadius.xl,
-      backgroundColor: `${colors.primary.main}08`,
-      paddingHorizontal: spacing.xs,
-      paddingVertical: spacing.xs,
-      // 移除阴影效果
-      shadowColor: 'transparent',
-      shadowOffset: { width: 0, height: 0 },
-      shadowOpacity: 0,
-      shadowRadius: 0,
-      elevation: 0,
     },
     cancelButton: {
-      backgroundColor: `${colors.primary.main}14`,
+      backgroundColor: `${colors.primary.main}12`,
       borderRadius: borderRadius.full,
       paddingHorizontal: spacing.md,
-      paddingVertical: spacing.xs,
+      paddingVertical: spacing.sm,
     },
     cancelText: {
       fontSize: fontSizes.md,
@@ -610,7 +601,7 @@ function createSearchScreenStyles(colors: AppColors) {
       marginBottom: spacing.sm,
     },
     sectionTitle: {
-      fontWeight: '600',
+      fontWeight: '700',
       color: colors.text.primary,
     },
     tagContainer: {
@@ -620,13 +611,14 @@ function createSearchScreenStyles(colors: AppColors) {
     tag: {
       flexDirection: 'row',
       alignItems: 'center',
-      backgroundColor: colors.background.paper,
-      borderRadius: borderRadius.lg,
-      borderWidth: 1,
-      borderColor: colors.divider,
+      backgroundColor: `${colors.primary.main}10`,
+      borderRadius: borderRadius.full,
+      borderWidth: 0,
     },
     tagText: {
       marginLeft: spacing.xs,
+      color: colors.primary.main,
+      fontWeight: '500',
     },
     userCard: {
       backgroundColor: colors.background.paper,