feat: add Express API base structure

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/index.ts

@@ -0,0 +1,9 @@
+import { app } from './app.js';
+import { env } from './config/env.js';
+
+const PORT = parseInt(env.PORT, 10);
+
+app.listen(PORT, () => {
+  console.log(`🚀 API Server running on http://localhost:${PORT}`);
+  console.log(`📊 Environment: ${env.NODE_ENV}`);
+});