[bn] Environment Variables

[bn] Create a `.env` file based on `.env.example`:

```bash
# Database
DATABASE_URL="postgresql://user:password@localhost:5432/prompts"

# Authentication (choose one provider)
# GitHub OAuth
AUTH_GITHUB_ID="your-github-client-id"
AUTH_GITHUB_SECRET="your-github-client-secret"

# Or Google OAuth
AUTH_GOOGLE_ID="your-google-client-id"
AUTH_GOOGLE_SECRET="your-google-client-secret"

# NextAuth
AUTH_SECRET="generate-a-random-secret"

# Optional: AI-powered semantic search
OPENAI_API_KEY="your-openai-api-key"
```