Code review s best practices

Proveď detailní code review následujícího [JAZYK] kódu. Zaměř se na:\n\n**1. Security Issues:**\n- Injection vulnerabilities\n- Authentication/authorization\n- Data validation\n- Sensitive data exposure\n\n**2. Performance:**\n- Time complexity\n- Space complexity\n- Database queries (N+1, indexes)\n- Caching opportunities\n\n**3. Code Quality:**\n- Naming conventions\n- Function length & complexity\n- DRY violations\n- SOLID principles\n\n**4. Testing:**\n- Test coverage gaps\n- Edge cases\n- Mock appropriateness\n\n**5. Documentation:**\n- Comments quality\n- API documentation\n- README completeness\n\n**Kód:**\n```[JAZYK]\n[KÓD]\n```\n\n**Output Format:** [DETAILED/SUMMARY]. Priority: [CRITICAL/HIGH/MEDIUM/LOW] pro každý finding.