Gate Rz Coins on correct-first-try-within-time-limit; match coin-flight animation to it

Credits were previously awarded on any first attempt regardless of
correctness or timing. The award now requires the first-ever attempt
to be correct (record.Attempt.IsCorrect) and submitted before the
adaptive per-question timer expired (new MetTimeLimit request field,
computed client-side from the same elapsed/target comparison that
already drives the visible countdown bar). The coin-flight animation
in question_player.gd now only plays when both conditions are met
(BlockSessionService.submit_core_attempt's existing "mastered" flag
plus met_time_limit), so the effect never promises a coin that isn't
actually earned.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

api/QuestionsApi/Controllers/QuestionsController.cs

@@ -175,7 +175,7 @@ public class QuestionsController : ControllerBase
             _metrics.AttemptDuplicate();
         }
         await _reviewQueue.AddFromFirstAttemptAsync(record.Attempt);
-        if (record.Inserted && !User.IsInRole("SUPER"))
+        if (record.Inserted && record.Attempt.IsCorrect && req.MetTimeLimit && !User.IsInRole("SUPER"))
             await _credits.AwardForFirstAnswerAsync(userId, record.Attempt.Id ?? "");
 
         var ratingOwner = Guid.NewGuid().ToString("N");