fix(quest/learner): draw turn-in '?' for in-log quests; learn turn-in NPC

Reverts the previous approach of stripping char.complete (which mutated
completed-quest data). Correct rule: a quest in the player's log is active
and should show its turn-in location regardless of the completed flag.

- AddFinisher now trusts the live quest log: if the quest is in
  currentQuestlog and not failed, the '?' finisher draws regardless of the
  (possibly stale, e.g. prior-prestige) char.complete flag. No completion
  data is modified. Reverts the AcceptQuest and QUEST_QUERY_COMPLETE strips.

- Learner: OnTargetChanged now learns quest-giver/turn-in NPC spawns
  (it previously only cached the GUID), so targeting a turn-in NPC records
  its location. OnQuestComplete/OnQuestTurnedIn fall back to the 'target'
  unit when the 'npc' gossip unit is already cleared, so the finisher NPC
  is reliably learned on turn-in.

selene 0 errors; busted 145 successes / same 7 pre-existing failures.

Compat/Compat.lua

@@ -734,15 +734,9 @@ end
 function QuestieCompat:QUEST_QUERY_COMPLETE(event)
     GetQuestsCompleted(Questie.db.char.complete)
 
-    local currentQuestlog = QuestiePlayer and QuestiePlayer.currentQuestlog
     local questId = next(Questie.db.char.complete)
     while questId do
-        -- Repeatable quests are never "complete" for availability purposes.
-        -- Also: a quest currently in the player's log is active, not turned in — the server's
-        -- completed list can still report a quest re-accepted after an Ascension prestige, and
-        -- that stale flag suppresses the turn-in '?' finisher and mislabels it "(Complete)".
-        -- Keep char.complete and the live quest log mutually exclusive.
-        if QuestieDB.IsRepeatable(questId) or (currentQuestlog and currentQuestlog[questId]) then
+        if QuestieDB.IsRepeatable(questId) then
             Questie.db.char.complete[questId] = nil
         end
         questId = next(Questie.db.char.complete, questId)