Replace manual world object creation with native CreateEntityInstance_WithAttachment API

Markers are now created via the game's high-level entity factory (0x6707c0)
which handles spatial registration, render setup, and lifecycle internally.
Removed ~300 lines of dead code: manual game object list insertion, A/B mode
switching, parity scanning, and model attachment wrappers.

Creation works (markers visible). Destruction still crashes — needs correct
destructor for entities created via CreateWorldUnit path (not DestroyWorldObjectAndRelease).

src/markers/addon/Markers.lua

@@ -6,7 +6,6 @@ MARKERS_VERSION = 1
 BINDING_HEADER_MARKERS = "Markers"
 
 local frame = CreateFrame("Frame")
-frame:RegisterEvent("ADDON_LOADED")
 frame:RegisterEvent("PLAYER_LOGIN")
 
 frame:SetScript("OnEvent", function()
@@ -19,27 +18,27 @@ SLASH_MARKERS1 = "/markers"
 SLASH_MARKERS2 = "/mark"
 SlashCmdList["MARKERS"] = function(msg)
     msg = string.lower(msg or "")
-    
+
     if msg == "" or msg == "help" then
         DEFAULT_CHAT_FRAME:AddMessage("|cff00ff00Markers|r commands:")
         DEFAULT_CHAT_FRAME:AddMessage("  /mark test - Toggle test marker at player position")
-        DEFAULT_CHAT_FRAME:AddMessage("  /mark pos - Show player position")
         DEFAULT_CHAT_FRAME:AddMessage("  /mark on - Create test marker")
         DEFAULT_CHAT_FRAME:AddMessage("  /mark off - Destroy test marker")
-    
+        DEFAULT_CHAT_FRAME:AddMessage("  /mark pos - Show player position")
+
     elseif msg == "test" or msg == "toggle" then
         TestMarkerToggle()
-    
+
     elseif msg == "on" or msg == "create" then
         TestMarkerCreate()
-    
+
     elseif msg == "off" or msg == "destroy" then
         TestMarkerDestroy()
-    
+
     elseif msg == "pos" or msg == "position" then
         local x, y, z = GetPlayerPosition()
         DEFAULT_CHAT_FRAME:AddMessage(string.format("Position: %.2f, %.2f, %.2f", x, y, z))
-    
+
     else
         DEFAULT_CHAT_FRAME:AddMessage("|cffff0000Unknown command:|r " .. msg)
     end