fix(lobby_transfer): restore transferPlayer beta API (Player.transfer does not exist in BDS 1.26)

Commit 81f84b5 misdiagnosed the mc-lobby crash loop and stripped the
@minecraft/server-admin@1.0.0-beta dependency, swapping in
player.transfer({hostname,port}). At runtime that throws
"player.transfer is not a function" the first time anyone steps on a
portal — the stable @minecraft/server API never exposed transfer() on
Player in BDS 1.26.14.

The real root cause of the original crash loop was unrelated: the
mc-lobby Docker volume had lost its vanilla behavior-pack collection
(vanilla_*, chemistry*, editor, server_library, …). Copying those back
from a healthy sibling volume fixed the boot crash; nothing in the
lobby_transfer pack needed to change. Restoring the beta transferPlayer
here brings lobby back in line with hub-return-addon, which has always
used this pattern successfully on jamie/lyla/mya.

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

lobby-addon/lobby_transfer_BP/manifest.json

@@ -26,6 +26,10 @@
       "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]