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/repositories/mongo/MongoChatRepository.ts

@@ -3,6 +3,7 @@ import {
   Conversation,
   CreateMessageDTO,
   GetMessagesOptions,
+  UpdateMessageDTO,
 } from "@caldav/shared";
 import { ChatRepository } from "../../services/interfaces";
 import { ChatMessageModel, ConversationModel } from "./models";
@@ -10,11 +11,15 @@ import { ChatMessageModel, ConversationModel } from "./models";
 export class MongoChatRepository implements ChatRepository {
   // Conversations
   async getConversationsByUser(userId: string): Promise<Conversation[]> {
-    throw new Error("Not implemented");
+    const conversations = await ConversationModel.find({ userId });
+    return conversations.map((c) => c.toJSON() as unknown as Conversation);
   }
 
   async createConversation(userId: string): Promise<Conversation> {
-    throw new Error("Not implemented");
+    const conversation = await ConversationModel.create({
+      userId,
+    });
+    return conversation.toJSON() as unknown as Conversation;
   }
 
   // Messages (cursor-based pagination)
@@ -22,13 +27,44 @@ export class MongoChatRepository implements ChatRepository {
     conversationId: string,
     options?: GetMessagesOptions,
   ): Promise<ChatMessage[]> {
-    throw new Error("Not implemented");
+    const limit = options?.limit ?? 20;
+    const query: Record<string, unknown> = { conversationId };
+
+    // Cursor: load messages before this ID (for "load more" scrolling up)
+    if (options?.before) {
+      query._id = { $lt: options.before };
+    }
+
+    // Fetch newest first, then reverse for chronological order
+    const docs = await ChatMessageModel.find(query)
+      .sort({ _id: -1 })
+      .limit(limit);
+
+    return docs.reverse().map((doc) => doc.toJSON() as unknown as ChatMessage);
   }
 
   async createMessage(
     conversationId: string,
     message: CreateMessageDTO,
   ): Promise<ChatMessage> {
-    throw new Error("Not implemented");
+    const repoMessage = await ChatMessageModel.create({
+      conversationId: conversationId,
+      sender: message.sender,
+      content: message.content,
+      proposedChange: message.proposedChange,
+    });
+    return repoMessage.toJSON() as unknown as ChatMessage;
+  }
+
+  async updateMessage(
+    messageId: string,
+    updates: UpdateMessageDTO,
+  ): Promise<ChatMessage | null> {
+    const doc = await ChatMessageModel.findByIdAndUpdate(
+      messageId,
+      { $set: updates },
+      { new: true },
+    );
+    return doc ? (doc.toJSON() as unknown as ChatMessage) : null;
   }
 }

apps/server/src/repositories/mongo/models/ChatModel.ts

@@ -80,6 +80,10 @@ const ChatMessageSchema = new Schema<
     proposedChange: {
       type: ProposedChangeSchema,
     },
+    respondedAction: {
+      type: String,
+      enum: ["confirm", "reject"],
+    },
   },
   {
     timestamps: true,