Add DTO validation for FederationCapabilities to ensure proper structure. - Create FederationCapabilitiesDto with class-validator decorators - Validate boolean types for capability flags - Validate string type for protocolVersion - Update IncomingConnectionRequestDto to use validated DTO - Add comprehensive unit tests for DTO validation Fixes #295 Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>