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/stores/user/UserManager.ts

@@ -14,6 +14,14 @@ import { createDedupe } from '../utils/requestDedupe';
 
 const dedupe = createDedupe(() => useUserManagerStore);
 
+// 将 fetchCurrentUserFromAPI 的判别结果转为 User | null。
+// 网络故障/认证失败时返回 null，由上层缓存兜底（避免空数据覆盖缓存）。
+// 注意：UserManager 只负责缓存，不触发登出，登出由 authStore 统一处理。
+async function fetchCurrentUserOrNull(): Promise<UserDTO | null> {
+  const result = await authService.fetchCurrentUserFromAPI();
+  return result.kind === 'user' ? result.user : null;
+}
+
 // ==================== UserManager 类 ====================
 
 class UserManager {
@@ -41,11 +49,11 @@ class UserManager {
     }
 
     return dedupe('users:current', async () => {
-      const user = await authService.fetchCurrentUserFromAPI();
-      const newEntry = createCacheEntry(user, DEFAULT_TTL.USER);
-      store.setCurrentUserEntry(newEntry);
-
+      const user = await fetchCurrentUserOrNull();
+      // 仅在拿到真实用户时刷新缓存；网络/认证失败时保留旧缓存，避免误清空
       if (user) {
+        const newEntry = createCacheEntry(user, DEFAULT_TTL.USER);
+        store.setCurrentUserEntry(newEntry);
         userCacheRepository.saveCurrent(user).catch(() => {});
         userCacheRepository.save(user).catch(() => {});
       }
@@ -56,11 +64,10 @@ class UserManager {
   private refreshCurrentUserInBackground(): void {
     dedupe('users:current:bg', async () => {
       const store = useUserManagerStore.getState();
-      const user = await authService.fetchCurrentUserFromAPI();
-      const newEntry = createCacheEntry(user, DEFAULT_TTL.USER);
-      store.setCurrentUserEntry(newEntry);
-
+      const user = await fetchCurrentUserOrNull();
       if (user) {
+        const newEntry = createCacheEntry(user, DEFAULT_TTL.USER);
+        store.setCurrentUserEntry(newEntry);
         userCacheRepository.saveCurrent(user).catch(() => {});
         userCacheRepository.save(user).catch(() => {});
       }