fix(transfer): use transferPlayer() beta API and enable experiments in level.dat

Switch from runCommand("transfer ...") to the @minecraft/server-admin
transferPlayer() function for reliable server-to-server transfers.
Enable Beta APIs experiment (gametest flag) in all 4 world level.dat files.
Add spawn protection to prevent transfer loops on arrival.

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

lobby-addon/lobby_transfer_BP/manifest.json

@@ -4,7 +4,7 @@
     "name": "Lobby Portal Transfer",
     "description": "Auto-transfers players when they step into portal areas",
     "uuid": "a1b2c3d4-1111-2222-3333-abcdef123456",
-    "version": [1, 0, 1],
+    "version": [1, 0, 3],
     "min_engine_version": [1, 21, 0]
   },
   "modules": [
@@ -12,14 +12,18 @@
       "type": "script",
       "language": "javascript",
       "uuid": "a1b2c3d4-4444-5555-6666-abcdef789012",
-      "version": [1, 0, 1],
+      "version": [1, 0, 3],
       "entry": "scripts/main.js"
     }
   ],
   "dependencies": [
     {
       "module_name": "@minecraft/server",
-      "version": "2.0.0"
+      "version": "1.17.0"
+    },
+    {
+      "module_name": "@minecraft/server-admin",
+      "version": "1.0.0-beta"
     }
   ]
 }