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/Quest/QuestManager.cs

@@ -1014,6 +1014,7 @@ namespace BaseGames.Quest
                 foreach (var qid in toFail)
                 {
                     _questStates[qid] = QuestStateEnum.Failed;
+                    _completedAtUtc[qid] = System.DateTimeOffset.UtcNow.ToUnixTimeSeconds();
                     _notifiedReadyQuests.Remove(qid);
                     OnQuestStateChanged?.Invoke(qid, QuestStateEnum.Active, QuestStateEnum.Failed);
                     Chan_QuestFailed?.Raise(qid);