fix(lobby_transfer): replace removed @minecraft/server-admin transferPlayer with stable Player.transfer

Bedrock 1.26 rejects the @minecraft/server-admin 1.0.0-beta dependency at
pack load, which was crashing mc-lobby on boot (exit 1 right after pack
stack + block-version logging). The transferPlayer helper has been part of
the stable @minecraft/server API as Player.transfer since 1.21, so we can
drop the server-admin import and dependency entirely.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lobby-addon/lobby_transfer_BP/manifest.json

@@ -26,10 +26,6 @@
       "module_name": "@minecraft/server",
       "version": "1.17.0"
     },
-    {
-      "module_name": "@minecraft/server-admin",
-      "version": "1.0.0-beta"
-    },
     {
       "uuid": "b2c3d4e5-1111-2222-3333-fedcba654321",
       "version": [1, 0, 0]