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/shared/database/index.ts

@@ -0,0 +1,58 @@
+import { drizzle } from "drizzle-orm/node-postgres";
+import { Pool } from "pg";
+import { config } from "../config/index.js";
+import { createChildLogger } from "../logger/index.js";
+
+const logger = createChildLogger("database");
+
+let pool: Pool | null = null;
+let db: ReturnType<typeof drizzle> | null = null;
+
+export async function initializeDatabase() {
+  if (db) {
+    logger.warn("Database already initialized");
+    return db;
+  }
+
+  const databaseUrl =
+    config.DATABASE_URL ||
+    `postgresql://${config.DATABASE_USER}${config.DATABASE_PASSWORD ? `:${config.DATABASE_PASSWORD}` : ""}@${config.DATABASE_HOST}:${config.DATABASE_PORT}/${config.DATABASE_NAME}`;
+
+  pool = new Pool({
+    connectionString: databaseUrl,
+  });
+
+  pool.on("error", (err) => {
+    logger.error({ err }, "Unexpected error on idle client");
+  });
+
+  try {
+    const client = await pool.connect();
+    client.release();
+    logger.info("Database connection successful");
+  } catch (err) {
+    logger.error({ err }, "Failed to connect to database");
+    throw err;
+  }
+
+  db = drizzle(pool);
+  return db;
+}
+
+export function getDatabase() {
+  if (!db) {
+    throw new Error(
+      "Database not initialized. Call initializeDatabase() first.",
+    );
+  }
+  return db;
+}
+
+export async function closeDatabase() {
+  if (pool) {
+    await pool.end();
+    pool = null;
+    db = null;
+    logger.info("Database connection closed");
+  }
+}