feat(tooltip): ElvUI style without ElvUI; source in secondary only; fix learner source label

- ElvUI tooltip style: new 'ElvUI tooltip style' option (General tab, on by
  default) skins GameTooltip/WorldMapTooltip/ItemRefTooltip/shopping tooltips
  and the secondary learner frame with ElvUI's transparent flat look (dark bg
  + thin 1px border) when ElvUI is not installed. Corrected the secondary
  frame fallback that used the chunky WoW border. No-op when ElvUI is loaded.

- Source attribution now shows ONLY inside the secondary learner tooltip when
  'Use secondary learner tooltip' is enabled; removed from the main NPC/object/
  item tooltip and gated off entirely when the secondary tooltip is disabled
  (map-pin source gated the same way).

- Fixed learner-learned pins mislabelled 'AscensionDB': GetPinDataSource is now
  mode-aware and returns 'Learner' in learner mode when the entity has a learner
  record, even if AscensionDB also curates it (curated coords are discarded by
  GetNPC/GetObject in learner mode anyway).

Test-neutral (145 successes / same 7 pre-existing failures + 1 error).

Modules/Tooltips/MapIconTooltip.lua

@@ -107,6 +107,9 @@ end
 --- the label is accurate, plus a Comms overlay when comms holds data for this id.
 local function _GetWorldMapDataSourceLine(pinData)
     if not Questie.db.profile.enableTooltipsSource then return nil end
+    -- Source attribution is tied to the secondary learner tooltip: only show it when that
+    -- option is enabled, and never otherwise (matches the unit-hover behaviour).
+    if Questie.db.profile.learnerTooltipUseSecondary ~= true then return nil end
     local src = pinData and pinData.DataSource
     local parts = {}
     if src then tinsert(parts, src) end