Add explicit write transactions and deterministic ordering tests

Endpoints/AdminWorkflowService.cs

@@ -13,6 +13,8 @@ internal sealed class AdminWorkflowService(AppDbContext db)
         state.ResultsOpen = request.ResultsOpen;
         state.UpdatedAt = DateTimeOffset.UtcNow;
 
+        await using var tx = await db.Database.BeginTransactionAsync();
+
         if (request.ResultsOpen)
         {
             await db.Players.ExecuteUpdateAsync(p => p.SetProperty(x => x.CurrentPhase, Phase.Results));
@@ -23,6 +25,7 @@ internal sealed class AdminWorkflowService(AppDbContext db)
         }
 
         await db.SaveChangesAsync();
+        await tx.CommitAsync();
         var currentState = await db.AppState.AsNoTracking().FirstAsync();
         return Results.Ok(new
         {
@@ -207,6 +210,8 @@ internal sealed class AdminWorkflowService(AppDbContext db)
 
     public async Task<IResult> ResetAsync()
     {
+        await using var tx = await db.Database.BeginTransactionAsync();
+
         await db.Votes.ExecuteDeleteAsync();
         await db.Suggestions.ExecuteDeleteAsync();
 
@@ -215,6 +220,7 @@ internal sealed class AdminWorkflowService(AppDbContext db)
         state.ResultsOpen = false;
         state.UpdatedAt = DateTimeOffset.UtcNow;
         await db.SaveChangesAsync();
+        await tx.CommitAsync();
 
         return Results.Ok(new
         {