refactor(core): distinguish network errors from auth failures and refactor real-time messaging pipeline

- Add isNetworkError() helper and FetchCurrentUserResult discriminated union to prevent logout on network failures
- Refactor authService to return { kind: 'user' } | { kind: 'auth_failed' } | { kind: 'network_error' }
- Update authStore to preserve login state on network errors, only logout on auth failures
- Replace WSMessageHandler with RealtimeIngestionPipeline for improved real-time message handling
- Remove MessageDeduplication service; add store-level idempotent addOrReplaceMessage for message dedup
- Add atomic systemUnreadCount operations to prevent race conditions
- Add SearchHeader component for consistent search UI across screens
- Add 'home' TabBar variant with underline style matching HomeScreen
- Add Jest test infrastructure and exclude tests from tsconfig
- Fix ChatScreen history lock being stuck when scrolling to latest messages
- Remove unused call_participant_joined/left WS event types

src/screens/message/components/ChatScreen/useChatScreen.ts

@@ -649,6 +649,17 @@ export const useChatScreen = (props?: ChatScreenProps) => {
     isBrowsingHistoryRef.current = browsing;
   }, []);
 
+  /**
+   * 无条件清除浏览历史锁与自动跟随抑制（动量滚动结束、layout settle、
+   * 轻触回到底部等场景使用）。区别于 handleReachLatestEdge，后者受加载锁保护。
+   */
+  const clearHistoryLock = useCallback(() => {
+    if (isBrowsingHistoryRef.current || suppressAutoFollowRef.current) {
+      isBrowsingHistoryRef.current = false;
+      suppressAutoFollowRef.current = false;
+    }
+  }, []);
+
   // 进入聊天详情后立即清未读（不依赖滚动位置）
   useEffect(() => {
     if (!conversationId) return;
@@ -1653,5 +1664,6 @@ export const useChatScreen = (props?: ChatScreenProps) => {
     handleReachLatestEdge,
     jumpToLatestMessages,
     setBrowsingHistory,
+    clearHistoryLock,
   };
 };