feat: add multi-world hub system with lobby portals and hub-return addon

Lobby addon detects players in portal zones at X: -15/0/15 and transfers
them to Jamie/Lyla/Mya survival worlds. Hub-return addon gives players a
recovery compass and chat commands (!hub, !lobby) to return to the lobby.

Includes docker-compose.yml for 4 Bedrock servers (lobby + 3 child worlds),
spark pet behavior/resource packs, and updated .gitignore.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

addon/spark_pet_RP/textures/item_texture.json

@@ -0,0 +1,21 @@
+{
+  "resource_pack_name": "spark_pet_RP",
+  "texture_name": "atlas.items",
+  "texture_data": {
+    "dragon_whistle": {
+      "textures": "textures/items/dragon_whistle"
+    },
+"dragon_egg": {
+      "textures": "textures/items/dragon_egg"
+    },
+    "dragon_toy": {
+      "textures": "textures/items/dragon_toy"
+    },
+    "dragon_bones": {
+      "textures": "textures/items/dragon_bones"
+    },
+    "dragon_gravestone": {
+      "textures": "textures/items/dragon_gravestone"
+    },
+  }
+}