Scale display player by switching from SSE to polling

app/routes/api.py

@@ -29,11 +29,15 @@ def _enforce_and_touch_display_session(display: Display, sid: str | None):
         return True, None
 
     cutoff = datetime.utcnow() - timedelta(seconds=SESSION_TTL_SECONDS)
-    DisplaySession.query.filter(
-        DisplaySession.display_id == display.id,
-        DisplaySession.last_seen_at < cutoff,
-    ).delete(synchronize_session=False)
-    db.session.commit()
+    # Cleanup old sessions. Avoid committing if nothing was deleted (saves write locks on SQLite).
+    deleted = (
+        DisplaySession.query.filter(
+            DisplaySession.display_id == display.id,
+            DisplaySession.last_seen_at < cutoff,
+        ).delete(synchronize_session=False)
+    )
+    if deleted:
+        db.session.commit()
 
     existing = DisplaySession.query.filter_by(display_id=display.id, sid=sid).first()
     if existing: