feat(messaging): implement three-tier reply message lazy loading with offline fallback

Add lazy loading pipeline for reply message previews that checks memory → SQLite → server in order, enabling offline hit and graceful degradation for deleted/inaccessible messages. Includes `getReplyMessage` API endpoint and `jumpToMessageSeq` helper for navigation to referenced messages.

feat(create): extract MomentComposer and LongPostComposer for dual posting modes

Refactor CreatePostScreen shell to delegate content editing to specialized composers based on postMode ('moment' or 'long'), enabling long posts with voting support. Add expandable FAB with mode selection on HomeScreen.

fix(navigation): use navigate instead of push to prevent duplicate chat instances

Replace router.push with router.navigate in notification bootstrap to avoid creating duplicate chat instances when already on the chat screen.

fix(ui): update author badge styling with proper text contrast

Change author badge background to use hex transparency and add dedicated text color for better readability on both light and dark themes.

chore: normalize filename handling in file uploads and improve file segment rendering

Use asset.name as authoritative filename, remove redundant shadows from file cards inside bubbles.

app/_layout.tsx

@@ -148,7 +148,10 @@ function NotificationBootstrap() {
 
           if (conversationId) {
             const isGroup = conversationType === 'group';
-            router.push(
+            // 使用 navigate 而非 push，避免：
+            // 1. 在已有聊天页上创建重复实例（用户需要退出两次）
+            // 2. 从帖子等页面打开聊天通知后返回到帖子（而非消息列表）
+            router.navigate(
               hrefs.hrefChat({
                 conversationId,
                 userId: isGroup ? undefined : senderId,
@@ -159,10 +162,10 @@ function NotificationBootstrap() {
               })
             );
           } else {
-            router.push(hrefs.hrefNotifications());
+            router.navigate(hrefs.hrefNotifications());
           }
         } else {
-          router.push(hrefs.hrefNotifications());
+          router.navigate(hrefs.hrefNotifications());
         }
       });