Add new API endpoints and clean up handler interfaces:
- groups/handlers.go: New lab group management API
* CRUD operations for lab groups
* Member management with role assignment (admin/member/viewer)
* Group listing and membership queries
- tokens/handlers.go: Token generation and validation endpoints
* Create access tokens for public task sharing
* Validate tokens for secure access
* Token revocation and cleanup
- routes.go: Refactor handler registration
* Integrate groups handler into WebSocket routes
* Remove nil parameters from all handler constructors
* Cleaner dependency injection pattern
- Handler interface cleanup across all modules:
* jobs/handlers.go: Remove unused nil privacyEnforcer parameter
* jupyter/handlers.go: Streamline initialization
* scheduler/handlers.go: Consistent constructor signature
* ws/handler.go: Add groups handler to dependencies
