Refactor monolithic modules and harden booking, email, and auth infrastructure.

Split oversized frontend API client, email service, and admin/booking pages into focused modules while preserving import surfaces, and add Redis-backed queues, stale booking cleanup, stronger auth, and scale deployment configs.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/db/index.ts

@@ -12,8 +12,11 @@ const dbType = process.env.DB_TYPE || 'sqlite';
 let db: ReturnType<typeof drizzleSqlite> | ReturnType<typeof drizzlePg>;
 
 if (dbType === 'postgres') {
+  // Cap connections per instance so that, when running multiple replicas,
+  // DB_POOL_MAX * replicas stays below the Postgres max_connections limit.
   const pool = new pg.Pool({
     connectionString: process.env.DATABASE_URL || 'postgresql://localhost:5432/spanglish',
+    max: Number(process.env.DB_POOL_MAX || 10),
   });
   db = drizzlePg(pool, { schema });
 } else {