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/call/callStore.ts

@@ -680,24 +680,6 @@ export const callStore = create<CallState>((set, get) => ({
       })
     );
 
-    unsubs.push(
-      wsService.on('call_participant_joined', (msg) => {
-        console.log('[CallStore] Participant joined:', msg.user_id);
-        const { currentCall } = get();
-        if (!currentCall || currentCall.id !== msg.call_id) return;
-        get().addParticipant(msg.user_id, { name: msg.user_id });
-      })
-    );
-
-    unsubs.push(
-      wsService.on('call_participant_left', (msg) => {
-        console.log('[CallStore] Participant left:', msg.user_id, 'reason:', msg.reason);
-        const { currentCall } = get();
-        if (!currentCall || currentCall.id !== msg.call_id) return;
-        get().removeParticipant(msg.user_id);
-      })
-    );
-
     const cleanup = () => {
       cleanupResources();
       if (unsubInvited) {