Prisma + Neon: use @prisma/adapter-neon, do not hand-roll the driver

# Prisma + Neon: use the official adapter

## The trap
Older tutorials wire Prisma to Neon by installing `@neondatabase/serverless` and `ws` and hand-rolling a driver adapter. That was before `@prisma/adapter-neon` existed. Agents following stale training data still do this, and then fight version mismatches between the driver, the ws package, and Prisma.

## The rule
Neon's current Prisma guide says it plainly: do not install `@neondatabase/serverless` or `ws` as separate packages. The `@prisma/adapter-neon` package bundles everything needed.

```sh
npm install @prisma/client @prisma/adapter-neon dotenv
```

```ts
import { PrismaClient } from './generated/prisma';
import { PrismaNeon } from '@prisma/adapter-neon';
const adapter = new PrismaNeon({ connectionString: process.env.DATABASE_URL });
export const prisma = new PrismaClient({ adapter });
```

## Checklist
- One adapter package, no manual ws wiring.
- Pooled `DATABASE_URL` into the adapter (app traffic), direct string for the CLI.
- If a tutorial tells you to `neonConfig.webSocketConstructor = ws`, it predates the adapter; follow the current guide instead.