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_BP/items/anthrax_cat.json

@@ -0,0 +1,21 @@
+{
+  "format_version": "1.21.0",
+  "minecraft:item": {
+    "description": {
+      "identifier": "silverlabs:anthrax_cat",
+      "menu_category": {
+        "category": "items",
+        "group": "itemGroup.name.misc"
+      }
+    },
+    "components": {
+      "minecraft:max_stack_size": 16,
+      "minecraft:icon": {
+        "texture": "anthrax_cat"
+      },
+      "minecraft:entity_placer": {
+        "entity": "silverlabs:anthrax_cat"
+      }
+    }
+  }
+}