- Add active flag to Player model with idempotent ALTER TABLE migration - Filter inactive players from main attendance table and API - New /admin page with date generation (preview + bulk add) and player management (add/deactivate/reactivate) - New API endpoints: GET/POST /api/players, PATCH /api/players/<id> - Add Admin nav link on main page Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>