Add custom item models for various shops using paper as the base item

data/new_music/function/custom_items/register.mcfunction

@@ -0,0 +1,6 @@
+# Generic registration helper for custom item models.
+# This keeps the item namespace separate from the display model name.
+# Usage: function new_music:custom_items/register {item:"minecraft:paper", model:"city_under_siege6"}
+
+# The resource pack handles the visual model via the shared item selector.
+# This function exists as a general entry point for future custom items.