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/media/media.service.ts

@@ -0,0 +1,9 @@
+import { createChildLogger } from "../../shared/logger/index.js";
+
+const logger = createChildLogger("media.service");
+
+export class MediaService {
+  // TODO: Implement media service methods
+}
+
+export const mediaService = new MediaService();

services/backend/src/modules/media/routes/index.ts

@@ -0,0 +1,13 @@
+import type { Router } from "express";
+import express from "express";
+
+export function createMediaRouter(): Router {
+  const router = express.Router();
+
+  // TODO: Implement media routes
+  // GET /api/media/list
+  // POST /api/media/upload
+  // GET /api/media/:id
+
+  return router;
+}