fix(worldmap): persist button toggle; hook OnShow/OnHide; Mapster offset

- Refactor button positioning and visibility into _PositionMapButton and
  _RefreshMapButtonVisibility helpers. Single source of truth for both.
- WorldMapButton.Initialize now hooks OnShow/OnHide on WorldMapFrame so
  the button self-updates when the user opens/closes the world map.
  No more manual show/hide calls required from elsewhere in the code.
- Toggle(shouldShow) now persists to Questie.db.profile.mapShowHideEnabled
  and calls _RefreshMapButtonVisibility, so the user's choice survives
  /reload and is consistent with the world map's current visibility.
- Special-case Mapster offset: -50, -72.3 vs default -50, -40. Without
  this, the button overlapped Mapster's UI elements when both addons
  were loaded.
- Frame level set to 99 to ensure the button draws above other map
  elements.

All helpers are no-op-safe when mapButton is nil. IsAddOnLoaded
('Mapster') is optional — falls through to default offset if Mapster
is not loaded.

Modules/WorldMapButton/WorldMapButton.lua

@@ -15,8 +15,36 @@ local KButtons = QuestieCompat.KButtons or LibStub("Krowi_WorldMapButtons-1.4")
 
 local mapButton
 
+local function _PositionMapButton()
+    if not mapButton then return end
+
+    local anchor = WorldMapDetailFrame or WorldMapButton or WorldMapFrame
+    mapButton:SetParent(anchor)
+    mapButton:ClearAllPoints()
+    if IsAddOnLoaded and IsAddOnLoaded("Mapster") then
+        mapButton:SetPoint("TOPRIGHT", anchor, "TOPRIGHT", -50, -72.3)
+    else
+        mapButton:SetPoint("TOPRIGHT", anchor, "TOPRIGHT", -50, -40)
+    end
+    mapButton:SetFrameLevel(99)
+end
+
+local function _RefreshMapButtonVisibility()
+    if not mapButton then return end
+
+    _PositionMapButton()
+    if Questie.db.profile.mapShowHideEnabled and WorldMapFrame:IsVisible() then
+        mapButton:Show()
+    else
+        mapButton:Hide()
+    end
+end
+
 function WorldMapButton.Initialize()
     mapButton = KButtons:Add("QuestieWorldMapButtonTemplate", "BUTTON")
+    _RefreshMapButtonVisibility()
+    WorldMapFrame:HookScript("OnShow", _RefreshMapButtonVisibility)
+    WorldMapFrame:HookScript("OnHide", _RefreshMapButtonVisibility)
 
     Questie.WorldMap = {
         Button = mapButton
@@ -25,11 +53,8 @@ end
 
 ---@param shouldShow boolean
 function WorldMapButton.Toggle(shouldShow)
-    if shouldShow then
+    Questie.db.profile.mapShowHideEnabled = shouldShow
-        mapButton:Show()
+    _RefreshMapButtonVisibility()
-    else
-        mapButton:Hide()
-    end
 end
 
 QuestieWorldMapButtonMixin = {