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/ChatRepository.ts

@@ -5,11 +5,13 @@ import {
   CreateEventDTO,
   GetMessagesOptions,
   UpdateMessageDTO,
+  ConflictingEvent,
 } from "@calchat/shared";
 
 export interface ChatRepository {
   // Conversations
   getConversationsByUser(userId: string): Promise<Conversation[]>;
+  getConversationById(conversationId: string): Promise<Conversation | null>;
   createConversation(userId: string): Promise<Conversation>;
 
   // Messages (cursor-based pagination)
@@ -38,5 +40,8 @@ export interface ChatRepository {
     messageId: string,
     proposalId: string,
     event: CreateEventDTO,
+    conflictingEvents?: ConflictingEvent[],
   ): Promise<ChatMessage | null>;
+
+  getMessageById(messageId: string): Promise<ChatMessage | null>;
 }