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/entities/anthrax_cat.json

@@ -3,7 +3,7 @@
   "minecraft:entity": {
     "description": {
       "identifier": "silverlabs:anthrax_cat",
-      "is_spawnable": true,
+      "is_spawnable": false,
       "is_summonable": true,
       "is_experimental": false
     },