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/models/entity/dragon_toy.geo.json

@@ -0,0 +1,26 @@
+{
+  "format_version": "1.12.0",
+  "minecraft:geometry": [
+    {
+      "description": {
+        "identifier": "geometry.dragon_toy",
+        "texture_width": 16,
+        "texture_height": 16
+      },
+      "bones": [
+        {
+          "name": "body",
+          "pivot": [0, 2, 0],
+          "cubes": [
+            {
+              "origin": [-2, 0, -2],
+              "size": [4, 4, 4],
+              "uv": [0, 0],
+              "inflate": 0.5
+            }
+          ]
+        }
+      ]
+    }
+  ]
+}