feat(anthrax-cat): add craftable item, recipe, and inventory entry

- Custom item silverlabs:anthrax_cat with entity_placer — place cat by right-clicking ground
- Shaped recipe: 4 gold ingots + 1 red dye (cross pattern) at crafting table
- Recipe unlocks when player has a gold ingot
- Item appears in creative inventory under Items > Misc
- Item icon: 16x16 Maneki-neko pixel art
- Set is_spawnable: false on entity (use crafted item instead of spawn egg)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

addon/anthrax_cat_RP/textures/item_texture.json

@@ -0,0 +1,9 @@
+{
+  "resource_pack_name": "anthrax_cat_RP",
+  "texture_name": "atlas.items",
+  "texture_data": {
+    "anthrax_cat": {
+      "textures": "textures/items/anthrax_cat"
+    }
+  }
+}