fix: timezone-aware datetime for elapsed timer in screen API

backend/app/api/screen.py

@@ -8,7 +8,7 @@ from app.models.match import Match, MatchPlayer, MatchStatus
 from app.models.player import Player
 from app.models.tournament import Tournament, TournamentStatus
 from app.services.tournament import get_bracket_data
-from datetime import datetime
+from datetime import datetime, timezone
 
 router = APIRouter(prefix="/screen", tags=["screen"])
 
@@ -47,7 +47,11 @@ def get_court_display(court_id: int, db: Session = Depends(get_db)):
 
         elapsed = None
         if active_match.started_at:
-            elapsed = int((datetime.utcnow() - active_match.started_at).total_seconds())
+            now = datetime.now(timezone.utc)
+            started = active_match.started_at
+            if started.tzinfo is None:
+                started = started.replace(tzinfo=timezone.utc)
+            elapsed = int((now - started).total_seconds())
 
         match_data = {
             "id": active_match.id,
@@ -89,7 +93,7 @@ def get_court_display(court_id: int, db: Session = Depends(get_db)):
         },
         "active_match": match_data,
         "recent_matches": recent,
-        "timestamp": datetime.utcnow().isoformat(),
+        "timestamp": datetime.now(timezone.utc).isoformat(),
     }
 
 
@@ -152,5 +156,5 @@ def get_overview(db: Session = Depends(get_db)):
             }
             for i, p in enumerate(top_players)
         ],
-        "timestamp": datetime.utcnow().isoformat(),
+        "timestamp": datetime.now(timezone.utc).isoformat(),
     }