- Add @MaxLength(500) to BrainQueryDto.query and BrainQueryDto.search fields
- Create BrainSearchDto with validated q (max 500 chars) and limit (1-100) fields
- Update BrainController.search to use BrainSearchDto instead of raw query params
- Add defensive validation in BrainService.search and BrainService.query methods:
- Reject search terms exceeding 500 characters with BadRequestException
- Clamp limit to valid range [1, 100] for defense-in-depth
- Add comprehensive tests for DTO validation and service-level guards
- Update existing controller tests for new search method signature
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
