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/TooltipHandler.lua

@@ -329,11 +329,9 @@ function _QuestieTooltips:AddUnitDataToTooltip()
             end
         end
 
-        -- Data-source attribution (opt-in; internally gated and nil when source unknown).
-        local npcSourceLine = QuestieTooltips:GetDataSourceLine("m_" .. npcId)
-        if npcSourceLine then
-            GameTooltip:AddLine(npcSourceLine)
-        end
+        -- Data-source attribution is rendered by QuestieLearner's secondary tooltip frame
+        -- (only when the secondary learner tooltip is enabled), never inline in the main
+        -- tooltip — see _AddLearnedSpawnTooltipLine.
 
         local npcNum = tonumber(npcId)
         if npcNum then
@@ -400,11 +398,6 @@ function _QuestieTooltips:AddItemDataToTooltip()
                 self:AddLine(v)
             end
         end
-        -- Data-source attribution (opt-in; internally gated and nil when source unknown).
-        local itemSourceLine = QuestieTooltips:GetDataSourceLine("i_" .. (itemId or 0))
-        if itemSourceLine then
-            self:AddLine(itemSourceLine)
-        end
         QuestieTooltips.lastGametooltipCount = _QuestieTooltips:CountTooltip()
     end
     lastItemId = itemId;
@@ -459,14 +452,6 @@ function _QuestieTooltips:AddObjectDataToTooltip(name)
                 end
             end
         end
-        -- Data-source attribution for the hovered object (opt-in; nil when unknown).
-        local firstObjectId = lookup[1]
-        if firstObjectId then
-            local objSourceLine = QuestieTooltips:GetDataSourceLine("o_" .. firstObjectId)
-            if objSourceLine then
-                GameTooltip:AddLine(objSourceLine)
-            end
-        end
         if QuestieTooltips.ResizeTooltip then
             QuestieTooltips:ResizeTooltip(GameTooltip)
         end