feat(anthrax-cat): add Maneki-neko lucky cat decoration addon, remove easter egg

- New silverlabs:anthrax_cat entity: sitting cat with waving paw animation,
  idle body bob, look-at-player, fortune message + bell sound on interact
- Custom 64x64 texture (cream/white, red bib, gold coin, orange tabby patches)
- Custom geometry: body, head, ears, raised left arm, tail, bib, coin bones
- Removed easter egg addon mounts from all 4 servers (lobby + 3 child worlds)
- Anthrax Cat mounted on all 4 servers

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

addon/anthrax_cat_RP/render_controllers/anthrax_cat.render_controllers.json

@@ -0,0 +1,10 @@
+{
+  "format_version": "1.8.0",
+  "render_controllers": {
+    "controller.render.anthrax_cat": {
+      "geometry": "Geometry.default",
+      "materials": [{ "*": "Material.default" }],
+      "textures": ["Texture.default"]
+    }
+  }
+}