- Added backend controller for tournament stages with endpoints to get, upsert, and advance stages.
- Created database migration for new tables: tournament_stage and tournament_stage_advancement.
- Updated models for TournamentStage and TournamentStageAdvancement.
- Enhanced frontend components to manage tournament stages, including configuration for intermediate and final rounds.
- Implemented logic for saving and advancing tournament stages, including handling of pool rules and third place matches.
- Added error handling and loading states in the frontend for better user experience.