fix: check for a new version when the room socket reconnects

[madeofpendletonwool]

After #75 was deployed, a Syncphony box that already had the page open kept running the old web app. That build ignores device.command, so Make speaker said it was handing the speaker over, but nothing happened on the box.

The page only checked for a new service worker when it loaded, and then once an hour. A deploy restarts the server, which drops every room socket. So now the room socket looks for a new version whenever it reconnects:

• A box takes the new version by itself and reloads within moments.
• Other clients get the usual "A new version is ready" toast.

Testing

• Locally, end to end against the new build (Chrome via Playwright): a page paired as a box was stopped, then told to Make speaker from the owner's session. It claimed the speaker within about a second.
• typecheck, lint and all web tests pass.