feat: implement chat persistence with MongoDB

- Add full chat persistence to database (conversations and messages)
- Implement MongoChatRepository with cursor-based pagination
- Add getConversations/getConversation endpoints in ChatController
- Save user and assistant messages in ChatService.processMessage()
- Track respondedAction (confirm/reject) on proposed event messages
- Load existing messages on chat screen mount
- Add addMessages() bulk action and chatMessageToMessageData() helper to ChatStore
- Add RespondedAction type and UpdateMessageDTO to shared types

apps/server/src/controllers/ChatController.ts

@@ -4,6 +4,7 @@ import {
   CreateEventDTO,
   UpdateEventDTO,
   EventAction,
+  GetMessagesOptions,
 } from "@caldav/shared";
 import { ChatService } from "../services";
 import { AuthenticatedRequest } from "../middleware";
@@ -66,13 +67,43 @@ export class ChatController {
     req: AuthenticatedRequest,
     res: Response,
   ): Promise<void> {
-    throw new Error("Not implemented");
+    try {
+      const userId = req.user!.userId;
+      const conversations = await this.chatService.getConversations(userId);
+      res.json(conversations);
+    } catch (error) {
+      res.status(500).json({ error: "Failed to get conversations" });
+    }
   }
 
   async getConversation(
     req: AuthenticatedRequest,
     res: Response,
   ): Promise<void> {
-    throw new Error("Not implemented");
+    try {
+      const userId = req.user!.userId;
+      const { id } = req.params;
+      const { before, limit } = req.query as {
+        before?: string;
+        limit?: string;
+      };
+
+      const options: GetMessagesOptions = {};
+      if (before) options.before = before;
+      if (limit) options.limit = parseInt(limit, 10);
+
+      const messages = await this.chatService.getConversation(
+        userId,
+        id,
+        options,
+      );
+      res.json(messages);
+    } catch (error) {
+      if ((error as Error).message === "Conversation not found") {
+        res.status(404).json({ error: "Conversation not found" });
+      } else {
+        res.status(500).json({ error: "Failed to get conversation" });
+      }
+    }
   }
 }