Add mcrcon-rbw wrapper for Minecraft RCON

Wrapper that auto-authenticates via rbw (Bitwarden) for RCON access.
- Uses minecraft-rcon entry from Bitwarden
- Defaults to 10.0.0.165:25575 (LoadBalancer IP)
- Supports MCRCON_HOST/PORT overrides
- Interactive terminal mode when no args provided

Part of k3s-cluster-config bead k3s-cluster-config-byg

packages/default.nix

@@ -3,4 +3,5 @@
   tea-rbw = pkgs.callPackage ./tea-rbw {};
   app-launcher-server = pkgs.callPackage ./app-launcher-server {};
   claude-code = pkgs.callPackage ./claude-code {};
+  mcrcon-rbw = pkgs.callPackage ./mcrcon-rbw {};
 }