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_BP/blocks/dragon_basket.json

@@ -0,0 +1,36 @@
+{
+  "format_version": "1.21.0",
+  "minecraft:block": {
+    "description": {
+      "identifier": "silverlabs:dragon_basket",
+      "menu_category": {
+        "category": "items",
+        "group": "itemGroup.name.bed"
+      }
+    },
+    "components": {
+      "minecraft:geometry": "geometry.dragon_basket",
+      "minecraft:material_instances": {
+        "*": {
+          "texture": "dragon_basket",
+          "render_method": "alpha_test"
+        }
+      },
+      "minecraft:collision_box": {
+        "origin": [-7, 0, -7],
+        "size": [14, 5, 14]
+      },
+      "minecraft:selection_box": {
+        "origin": [-7, 0, -7],
+        "size": [14, 5, 14]
+      },
+      "minecraft:destructible_by_mining": {
+        "seconds_to_destroy": 1.0
+      },
+      "minecraft:destructible_by_explosion": {
+        "explosion_resistance": 2.0
+      },
+      "minecraft:map_color": "#8B5E3C"
+    }
+  }
+}