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.

Modules/Quest/QuestieQuest.lua

@@ -500,15 +500,6 @@ function QuestieQuest:AcceptQuest(questId)
         -- shows again (covers re-doing the quest after abandon or an Ascension prestige).
         QuestieQuest:ClearLootedSpawns(questId)
 
-        -- An accepted quest is active, NOT completed-and-turned-in. On Ascension a quest
-        -- completed in a previous prestige stays in char.complete; when re-accepted the stale
-        -- flag made Questie treat it as done — the turn-in '?' finisher was suppressed
-        -- (AddFinisher requires `not char.complete[questId]`) and it showed "(Complete)".
-        -- Clear it so the quest tracks/finishes normally again.
-        if Questie.db.char.complete then
-            Questie.db.char.complete[questId] = nil
-        end
-
         -- If any of these flags exist, this quest was previously accepted and may
         -- have stale completion state (e.g. complete-then-abandon-then-reaccept leaves
         -- quest.isComplete=true, WasComplete=true). Only check quest-object flags
@@ -1295,7 +1286,13 @@ function QuestieQuest:AddFinisher(quest)
 
     local complete = QuestieDB.IsComplete(questId)
 
-    if (QuestiePlayer.currentQuestlog[questId] and (IsQuestFlaggedCompleted(questId) == false) and (complete == 1 or complete == 0) and (not Questie.db.char.complete[questId])) then
+    -- A quest in the player's log is active and NOT yet turned in, so its turn-in finisher
+    -- should always be drawable regardless of the char.complete flag. On Ascension a quest
+    -- completed in a previous prestige stays flagged in char.complete; when re-accepted it is
+    -- active again, and gating the finisher on char.complete (the old `IsQuestFlaggedCompleted
+    -- == false and not char.complete` checks) wrongly suppressed the '?' at the turn-in NPC.
+    -- Trust the live quest log instead. (complete == -1 is a failed quest, so exclude it.)
+    if (QuestiePlayer.currentQuestlog[questId] and (complete == 1 or complete == 0)) then
         local finisher, key
 
         if quest.Finisher ~= nil then