refactor: Round 53 remove all legacy backward-compatibility code

- QuestSO: remove giverNpcId, prerequisiteQuests/Flags/FlagsLogic, failCondition,
  conditionFlags, npcDialogueKey fields; simplify GiverNpcId property to giverNpc?.npcId;
  clean ValidatePrerequisiteCycles/HasPrerequisiteCycle to use prerequisites.questDependencies;
  remove ValidateBranchDialogueKeys migration warning block; clean QuestPrerequisite doc
- QuestManager: remove OnLoad DataVersion 1/2 migration paths (ProgressCounts, hasNewFormat/
  useNewFormat); remove CheckQuestDepsAndFlags old-field fallback (prerequisiteQuests/Flags);
  remove UnlockBranches conditionFlags fallback; remove DispatchEvent failCondition fallback;
  fix ValidatePrerequisites DFS to scan prerequisites.questDependencies
- SaveData: remove ProgressCounts (Obsolete), ObjectiveIndex (unused), GiverNpcId (never
  written) fields from QuestState; simplify DataVersion doc comment
- QuestSOEditor: replace migration-only editor with minimal DrawDefaultInspector
- QuestModule: update all prerequisiteQuests/conditionFlags/npcDialogueKey/failCondition
  references to canonical new fields; update ValidateBranchFlags check 10
- FlagAuditModule: replace conditionFlags/prerequisiteFlags scans with conditionFlagEntries/
  prerequisites.flagCondition.flags
- NpcSO: remove QuestSO.giverNpcId reference from npcId tooltip
- NpcAffinityEvent/RewardSO: update doc comments to reference giverNpc instead of giverNpcId

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

Assets/_Game/Scripts/Quest/NpcAffinityEvent.cs

@@ -10,7 +10,8 @@ namespace BaseGames.Quest
     [System.Serializable]
     public struct NpcAffinityEvent
     {
-        /// <summary>发生好感度变化的 NPC ID（与 QuestSO.giverNpcId 保持一致）。</summary>
+        /// <summary>
+        /// NPC 好感度变化的 NPC ID（与 QuestSO.giverNpc.npcId 保持一致）。</summary>
         public string npcId;
         /// <summary>好感度变化量（正值=增加，负值=减少）。</summary>
         public int    delta;