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/manifest.json

@@ -0,0 +1,17 @@
+{
+  "format_version": 2,
+  "header": {
+    "name": "Anthrax Cat RP",
+    "description": "Anthrax Cat (Maneki-neko) textures, model, and animations",
+    "uuid": "c3d4e5f6-a7b8-9012-cdef-123456789012",
+    "version": [1, 0, 0],
+    "min_engine_version": [1, 21, 0]
+  },
+  "modules": [
+    {
+      "type": "resources",
+      "uuid": "d4e5f6a7-b8c9-0123-defa-234567890123",
+      "version": [1, 0, 0]
+    }
+  ]
+}