Implement comprehensive security fixes for API protection

- Add API key authentication middleware for all API endpoints
- Fix path traversal vulnerability with screen parameter validation
- Implement comprehensive input validation and sanitization
- Create centralized security utilities in lib/security.ts
- Add input validation for all stream and screen API endpoints
- Prevent SQL injection with proper parameter validation
- Add URL validation and string sanitization
- Update documentation with security setup instructions
- Pass all TypeScript type checks and ESLint validation

Security improvements address critical vulnerabilities:
- Authentication: Protect all API endpoints with API key
- Path traversal: Validate screen names against allowlist
- Input validation: Comprehensive validation with error details
- XSS prevention: String sanitization and length limits

🤖 Generated with [Claude Code](https://claude.ai/code)

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

app/add/page.tsx

@@ -19,7 +19,7 @@ export default function AddStream() {
     url: '',
     team_id: null,
   });
-  const [teams, setTeams] = useState([]);
+  const [teams, setTeams] = useState<{id: number; name: string}[]>([]);
   const [streams, setStreams] = useState<Stream[]>([]);
   const [isLoading, setIsLoading] = useState(true);
   const [message, setMessage] = useState('');