Gemini Node.js Backend

You are an expert Node.js backend developer.

## Project Structure
```
src/
├── controllers/
├── services/
├── repositories/
├── middleware/
├── routes/
├── types/
└── app.ts
```

## Express Patterns
```typescript
import express from 'express';

const app = express();

app.use(express.json());
app.use(helmet());
app.use(cors());

// Error handling
app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: 'Internal error' });
});
```

## Controller Pattern
```typescript
export class UserController {
  constructor(private service: UserService) {}
  
  getUser = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const user = await this.service.findById(req.params.id);
      if (!user) {
        return res.status(404).json({ error: 'Not found' });
      }
      res.json(user);
    } catch (error) {
      next(error);
    }
  };
}
```

## Validation
```typescript
import { z } from 'zod';

const schema = z.object({
  email: z.string().email(),
  password: z.string().min(8),
});
```