implement frontend skeleton with tab navigation and service layer

- Add tab-based navigation (Chat, Calendar) using Expo-Router
- Create auth screens (login, register) as skeletons
- Add dynamic routes for event detail and note editing
- Implement service layer (ApiClient, AuthService, EventService, ChatService)
- Add Zustand stores (AuthStore, EventsStore) for state management
- Create EventCard and EventConfirmDialog components
- Update CLAUDE.md with new frontend architecture documentation
- Add Zustand and FlashList to technology stack

apps/client/src/components/EventCard.tsx

@@ -0,0 +1,24 @@
+import { View, Text, Pressable } from 'react-native';
+import { CalendarEvent } from '@caldav/shared';
+
+type EventCardProps = {
+  event: CalendarEvent;
+  onPress?: (event: CalendarEvent) => void;
+};
+
+const EventCard = ({ event: _event, onPress: _onPress }: EventCardProps) => {
+  // TODO: Display event title, time, and description preview
+  // TODO: Handle onPress to navigate to EventDetailScreen
+  // TODO: Style based on event type or time of day
+  throw new Error('Not implemented');
+
+  return (
+    <Pressable>
+      <View>
+        <Text>EventCard - Not Implemented</Text>
+      </View>
+    </Pressable>
+  );
+};
+
+export default EventCard;

apps/client/src/components/EventConfirmDialog.tsx

@@ -0,0 +1,36 @@
+import { View, Text, Modal, Pressable } from 'react-native';
+import { CreateEventDTO } from '@caldav/shared';
+
+type EventConfirmDialogProps = {
+  visible: boolean;
+  proposedEvent: CreateEventDTO | null;
+  onConfirm: () => void;
+  onReject: () => void;
+  onClose: () => void;
+};
+
+const EventConfirmDialog = ({
+  visible: _visible,
+  proposedEvent: _proposedEvent,
+  onConfirm: _onConfirm,
+  onReject: _onReject,
+  onClose: _onClose,
+}: EventConfirmDialogProps) => {
+  // TODO: Display proposed event details (title, time, description)
+  // TODO: Confirm button calls onConfirm and closes dialog
+  // TODO: Reject button calls onReject and closes dialog
+  // TODO: Close button or backdrop tap calls onClose
+  throw new Error('Not implemented');
+
+  return (
+    <Modal visible={false} transparent animationType="fade">
+      <View>
+        <Pressable>
+          <Text>EventConfirmDialog - Not Implemented</Text>
+        </Pressable>
+      </View>
+    </Modal>
+  );
+};
+
+export default EventConfirmDialog;