fix(learner): learner-only mode shows only learner data

Three-mode spawn-merge semantics:
- Learner: discard npcDataOverrides (which AscensionDB's _Asc_MergeInto
  populates with curated coords). GetNPC returns learnerRecord only.
  _ApplyNpcLiveUpdate and object-spawn injection use IsAscensionProtected
  (mode-dependent) so learner coords pass through in learner mode.
- Auto: static DB primary, learner fills gaps. Curated spawns protected.
- Static: base DB only.

Also removes the allowSpawnMerge bypass that was the original hole
letting learner coords leak into curated spawns in auto mode.

Database/QuestieDB.lua

@@ -2277,6 +2277,10 @@ function QuestieDB:GetNPC(npcId)
         if not rawdata then
             rawdata = override
         end
+        -- Learner mode: discard any curated coords that AscensionDB's
+        -- _Asc_MergeInto wrote into npcDataOverrides. The learner's own
+        -- coords come from rawdata (learnerRecord), not from the override.
+        override = nil
     else
         rawdata = QuestieDB.QueryNPC(npcId, QuestieDB._npcAdapterQueryOrder)
         if not rawdata and learnerRecord and mode == "auto" then