Stop phase polling writes unless state changes

Endpoints/EndpointHelpers.cs

@@ -39,24 +39,28 @@ internal static class EndpointHelpers
 
         var state = await db.AppState.FirstAsync();
 
+        var changed = false;
+
         // Auto-upgrade any legacy Reveal phase to Vote to avoid blank screens
         if (player.CurrentPhase == Phase.Reveal)
         {
             player.CurrentPhase = Phase.Vote;
+            changed = true;
         }
 
         // Keep phases aligned with results availability
         if (state.ResultsOpen && player.CurrentPhase != Phase.Results)
         {
             player.CurrentPhase = Phase.Results;
+            changed = true;
         }
         else if (!state.ResultsOpen && player.CurrentPhase == Phase.Results)
         {
             player.CurrentPhase = Phase.Vote;
             player.VotesFinal = false;
+            changed = true;
         }
 
-        var changed = db.ChangeTracker.HasChanges();
         if (changed)
         {
             await db.SaveChangesAsync();