feat(contacts): integrate contacts into Todo and Calendar apps

- Add ContactSelector, ContactBadge, ContactAvatar to shared-ui
- Add ContactsClient API service to shared-auth
- Add ContactReference, ContactSummary types to shared-types
- Todo: Add assignee and involvedContacts to tasks with UI in TaskEditModal
- Todo: Display contacts in TaskItem and KanbanTaskCard
- Calendar: Add AttendeeSelector with RSVP status support
- Calendar: Integrate attendees in EventForm
- Calendar: Add task drag-drop to calendar views (Day/Week/MultiDay)
- Contacts: Add ContactTasks component to show related tasks
- Backend: Add findByContact endpoint to Todo task service
- UI polish: glassmorphism styling, keyboard navigation, auto-focus

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/calendar/packages/shared/src/types/event.ts

@@ -1,10 +1,21 @@
+/**
+ * Event attendee RSVP status
+ */
+export type AttendeeStatus = 'accepted' | 'declined' | 'tentative' | 'pending';
+
 /**
  * Event attendee information
  */
 export interface EventAttendee {
 	email: string;
 	name?: string;
-	status?: 'accepted' | 'declined' | 'tentative' | 'pending';
+	status?: AttendeeStatus;
+	/** Contact reference for linked contacts */
+	contactId?: string;
+	/** Cached photo URL from contact */
+	photoUrl?: string;
+	/** Cached company from contact */
+	company?: string;
 }
 
 /**