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>

lobby-addon/lobby_transfer_BP/manifest.json

@@ -0,0 +1,25 @@
+{
+  "format_version": 2,
+  "header": {
+    "name": "Lobby Portal Transfer",
+    "description": "Auto-transfers players when they step into portal areas",
+    "uuid": "a1b2c3d4-1111-2222-3333-abcdef123456",
+    "version": [1, 0, 1],
+    "min_engine_version": [1, 21, 0]
+  },
+  "modules": [
+    {
+      "type": "script",
+      "language": "javascript",
+      "uuid": "a1b2c3d4-4444-5555-6666-abcdef789012",
+      "version": [1, 0, 1],
+      "entry": "scripts/main.js"
+    }
+  ],
+  "dependencies": [
+    {
+      "module_name": "@minecraft/server",
+      "version": "2.0.0"
+    }
+  ]
+}