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/core/events/EventBus.ts

@@ -5,9 +5,7 @@ export type AppEvent =
   | { type: 'NAVIGATE_BACK' }
   | { type: 'SHOW_VERIFICATION_MODAL' }
   | { type: 'VIBRATE'; payload: { type: 'message' | 'group_message' | 'call' } }
-  | { type: 'SHOW_TOAST'; payload: { message: string; type: 'success' | 'error' | 'info' } }
-  | { type: 'AUTH_LOGOUT' }
-  | { type: 'AUTH_LOGIN'; payload: { userId: string } };
+  | { type: 'AUTH_LOGOUT' };
 
 class EventBusClass {
   private subscribers: Set<Subscriber<AppEvent>> = new Set();