Adds schemas/roomodes.json that accurately reflects the actual .roomodes
format as defined in packages/types/src/mode.ts. The schema supports:
- All CustomMode properties including optional description and source
- Tuple-style group entries like ["edit", { fileRegex, description }]
- All five tool groups: read, edit, command, mcp, modes
Also adds comprehensive tests validating the schema against valid and
invalid configurations.
Closes#11790
