feat(pet): add Hey Hey chicken pet addon

Tameable white chicken modelled on Hey Hey from Moana — custom plump
geometry, waddly walk/peck animations, hatching egg item, and vanilla
chicken sounds. Mounted on all 4 servers via docker-compose.

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

addon/heyhe_pet_RP/textures/item_texture.json

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