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>

CLAUDE.md

@@ -16,6 +16,16 @@ Four Bedrock servers on `10.0.0.247`, connected via native `/transfer` (no proxy
 Players connect to `10.0.0.247:19132` (lobby) and use portal zones to transfer to child worlds.
 Child worlds have a hub-return addon (compass, `!hub`/`!lobby` commands, portal zone) to transfer back.
 
+### Transfer Mechanism
+
+Transfers use `@minecraft/server-admin` beta API (`transferPlayer()` function). This requires:
+- **Beta APIs experiment** enabled in each world's `level.dat` (`gametest` experiment flag)
+- `@minecraft/server-admin` v1.0.0-beta dependency in manifest.json
+- `permissions.json` allowing `@minecraft/server-admin`
+
+The behavior packs are **bind-mounted** from the host project directory into Docker containers.
+Deploy path on server: `/home/sysadmin/minecraft-multiworld/`
+
 ## Connection
 
 The mc-ai-bridge runs at `10.0.0.247`: