refactor: split monolith into 3 microservices (frontend, backend, discord-gateway)

- Extract services into services/{frontend,backend,discord-gateway}
- Create packages/shared/ for shared logger, errors, utils, types
- Setup Modular MVC pattern in backend (controller→service→repository)
- Setup event-driven architecture in discord-gateway with Redis pub/sub
- Move Docker files to infra/docker/ with per-service Dockerfiles
- Update docker-compose.yml to use Traefik-only routing (no port exposes)
- Update GitHub Actions deploy workflow for multi-service matrix build
- Fix all import paths and resolve type errors across all services
- All 3 services pass tsc --noEmit clean

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/backend/src/modules/messages/messages.service.ts

@@ -0,0 +1,50 @@
+import { NotFoundError, ValidationError } from "../../shared/errors/index.js";
+import { createChildLogger } from "../../shared/logger/index.js";
+import { messagesRepository } from "./messages.repository.js";
+import type { MessageQuery } from "./messages.schema.js";
+
+const logger = createChildLogger("messages.service");
+
+export class MessagesService {
+  async listMessages(query: MessageQuery) {
+    if (!query.channelId && !query.guildId) {
+      throw new ValidationError("Either channelId or guildId is required");
+    }
+
+    logger.debug({ query }, "Listing messages");
+    return messagesRepository.findMany(query);
+  }
+
+  async getMessagesByChannel(channelId: string, query: MessageQuery) {
+    if (!channelId) {
+      throw new ValidationError("channelId is required");
+    }
+
+    logger.debug({ channelId, query }, "Getting messages by channel");
+    return messagesRepository.findByChannel(channelId, query);
+  }
+
+  async getMessageById(id: string) {
+    if (!id) {
+      throw new ValidationError("message ID is required");
+    }
+
+    const message = await messagesRepository.findById(id);
+    if (!message) {
+      throw new NotFoundError(`Message with ID ${id} not found`);
+    }
+
+    return message;
+  }
+
+  async getAttachmentsByChannel(channelId: string, query: MessageQuery) {
+    if (!channelId) {
+      throw new ValidationError("channelId is required");
+    }
+
+    logger.debug({ channelId, query }, "Getting attachments by channel");
+    return messagesRepository.getAttachmentsByChannel(channelId, query);
+  }
+}
+
+export const messagesService = new MessagesService();