Add REST API endpoints for court management and availability:
- GET/POST /api/courts for listing and creating courts
- GET/PUT/DELETE /api/courts/[id] for single court operations
- GET /api/courts/[id]/availability for time slot availability
- GET /api/sites for listing organization sites
Features include organization-based filtering, role-based access control,
premium pricing for evening/weekend slots, and booking conflict detection.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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