The relay keeps the turns and the hold state under FORGE_APP_DATA, so a restart restores the queue, the driver and a held arm #252

Split from #233, piece 2 of 2. It builds on Turns' file option from piece 1.

Done:

• [ ] Software/so101/src/lobby.ts (and bench/fake-serve.ts, which runs the app) pass a turns file under FORGE_APP_DATA, beside the other state.
• [ ] The held or E-stop state is persisted the same way and restored on start. A held arm stays held after a restart, and nothing un-holds it on its own.
• [ ] A test in the style of src/admin-restart.test.ts: stop and start on the same data, and the queue, the driver and the held state are as they were.
• [ ] forge.json is untouched. bun --cwd Software/so101 test passes.