Create NestJS Auth Guard Middleware

**Description:**  
Create middleware to guard protected routes using JWT validation.

**Requirements:**  
- Use `@nestjs/passport` with `PassportStrategy(JwtStrategy)`
- Inject user into Request object
- Middleware must support global guard usage via `@UseGuards(AuthGuard)`

**Acceptance Criteria:**  
- Any protected route must require a valid token
- Invalid tokens return 401