refactor(ui): redesign TabBar to border-bottom indicator style

- Remove pill container styling with shadows and rounded corners
- Simplify tab styling and reduce font weights
- Change active indicator from 20px to span 50% width
- Add channel tag display to PostDetailScreen
- Simplify SafeAreaView edge handling in embedded screens

src/screens/home/PostDetailScreen.tsx

@@ -1140,6 +1140,18 @@ export const PostDetailScreen: React.FC = () => {
           </View>
         )}
 
+        {/* 所属板块 */}
+        {!!post.channel?.name && (
+          <View style={[styles.channelTagContainer, { marginTop: responsiveGap }]}>
+            <View style={styles.channelTag}>
+              <MaterialCommunityIcons name="tag-outline" size={11} color={colors.primary.main} />
+              <Text style={styles.channelTagText} numberOfLines={1}>
+                {post.channel.name}
+              </Text>
+            </View>
+          </View>
+        )}
+
         {/* 发帖时间和浏览量 - 放在图片下方 */}
         <View style={[styles.postMetaInfo, { marginTop: responsiveGap }]}>
           <View style={styles.metaInfoMain}>
@@ -2226,6 +2238,27 @@ function createPostDetailStyles(colors: AppColors) {
     marginTop: spacing.md,
     textAlign: 'center',
   },
+  // 所属板块标签
+  channelTagContainer: {
+    flexDirection: 'row',
+    alignItems: 'center',
+  },
+  channelTag: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    maxWidth: 140,
+    paddingHorizontal: 6,
+    paddingVertical: 2,
+    borderRadius: borderRadius.sm,
+    backgroundColor: `${colors.primary.main}12`,
+    gap: 4,
+  },
+  channelTagText: {
+    fontSize: fontSizes.xs,
+    color: colors.primary.main,
+    fontWeight: '600',
+    flexShrink: 1,
+  },
   // 评论加载更多样式
   commentsLoadingFooter: {
     paddingVertical: spacing.md,