fix: Round 54 priority dequeue, onComplete callback, prerequisiteObjectiveId validation, localizationTable guard, FailQuest timestamp, remove empty ValidateBranchDialogueKeys

- DialogueManager.EndDialogue: dequeue by max-priority index instead of FIFO index-0
- DialogueManager.EndDialogue: fire _onCompleteCallback on normal end (was only in ForceEnd)
- NpcSO.OnValidate: auto-restore localizationTable to 'UI' if cleared
- QuestSO.ValidateObjectiveIds: validate prerequisiteObjectiveId references exist in same quest
- QuestSO.OnValidate: remove call to empty ValidateBranchDialogueKeys stub + remove the stub itself
- QuestManager.DispatchEvent toFail loop: write _completedAtUtc timestamp on quest failure

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Assets/_Game/Scripts/Dialogue/DialogueManager.cs

@@ -432,11 +432,19 @@ namespace BaseGames.Dialogue
             if (!string.IsNullOrEmpty(npcId))
                 _onNpcDialogueCompleted?.Raise(npcId);
 
-            // 自动播放队首等待中的对话（脚本触发的连续序列）
+            // 触发一次性完成回调（正常结束和强制中断均触发）
+            var cb = _onCompleteCallback;
+            _onCompleteCallback = null;
+            cb?.Invoke();
+
+            // 自动播放优先级最高的等待中对话（保证高优先级对话不被低优先级插队）
             if (_pending.Count > 0)
             {
-                var item = _pending[0];
-                _pending.RemoveAt(0);
+                int best = 0;
+                for (int i = 1; i < _pending.Count; i++)
+                    if (_pending[i].priority > _pending[best].priority) best = i;
+                var item = _pending[best];
+                _pending.RemoveAt(best);
                 PlayImmediate(item.seq, item.npcId, item.priority);
             }
         }