refactor: improve AI event handling and conflict display in chat

- AI fetches events on-demand via callbacks for better efficiency
- Add conflict detection with warning display when proposing overlapping events
- Improve event search and display in chat interface
- Load full chat history for display while limiting AI context

apps/server/src/services/interfaces/AIProvider.ts

@@ -1,14 +1,21 @@
 import {
-  CalendarEvent,
   ChatMessage,
   ProposedEventChange,
+  ExpandedEvent,
+  CalendarEvent,
 } from "@calchat/shared";
 
 export interface AIContext {
   userId: string;
   conversationHistory: ChatMessage[];
-  existingEvents: CalendarEvent[];
   currentDate: Date;
+  // Callback to load events from a specific date range
+  // Returns ExpandedEvent[] with occurrenceStart/occurrenceEnd for recurring events
+  fetchEventsInRange: (startDate: Date, endDate: Date) => Promise<ExpandedEvent[]>;
+  // Callback to search events by title
+  searchEvents: (query: string) => Promise<CalendarEvent[]>;
+  // Callback to fetch a single event by ID
+  fetchEventById: (eventId: string) => Promise<CalendarEvent | null>;
 }
 
 export interface AIResponse {