feat: Rebuild as Court Manager Dashboard v2

- Complete rewrite for single Court Manager user
- Feature 1: Player Management (CRUD, ELO, skill level)
- Feature 2: Court Reservation (timeline, override)
- Feature 3: Match Event Builder (3-step wizard)
  - Step 1: Event setup with player selection + stage calculator
  - Step 2: Stage configurator (Open/Skill/RR/Tournament)
  - Step 3: Auto bracket generation
- Feature 4: Live Court View (main dashboard, 2x2 grid)
- Event Control: score entry, bracket advancement, court assignment
- Screen view: TV display per court (/screen/:id)
- Seed: 8 players, 4 courts, 1 completed + 1 active event
- Routes: / players courts events events/new events/:id screen/:id

backend/app/routers/admin.py

@@ -0,0 +1,16 @@
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+from ..database import get_db
+from ..models import Base
+from ..database import engine
+import subprocess, sys
+
+router = APIRouter(prefix="/api/admin", tags=["admin"])
+
+
+@router.post("/seed")
+def seed_data(db: Session = Depends(get_db)):
+    """Re-seed all demo data"""
+    import subprocess, sys
+    result = subprocess.run([sys.executable, "/app/seed.py"], capture_output=True, text=True)
+    return {"ok": result.returncode == 0, "output": result.stdout[-500:], "error": result.stderr[-200:] if result.stderr else None}