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/animations/dragon_gravestone.animation.json

@@ -0,0 +1,18 @@
+{
+  "format_version": "1.8.0",
+  "animations": {
+    "animation.dragon_gravestone.idle": {
+      "loop": true,
+      "animation_length": 4.0,
+      "bones": {
+        "stone": {
+          "scale": {
+            "0.0": [1, 1, 1],
+            "2.0": [1, 1.02, 1],
+            "4.0": [1, 1, 1]
+          }
+        }
+      }
+    }
+  }
+}