feature: redesign the edge worker status and storage check

[lukepolo]

• New status panel shared by the Playcast edge relay (Streaming) and the Backblaze worker (Demos): a signal meter and status (online, needs attention, offline, not set up), the endpoint, when it was checked, and a link to the setup guide when something needs doing.
• The Backblaze worker status is a real check: the worker's /demo/_health reports whether Backblaze accepts its keys (feature: cloudflare workers and deploy scripts 5stack-panel#634). An older worker shows as needing an update.
• Test Upload / Test Download are now one storage check: write, read back (by the panel, via the new testDownload action in feature: storage check reads the test file back api#431), then the worker. Each step shows its result and timing; why a step failed goes in a note underneath.
• Transitions: the track fills toward the next step, steps and results fade in, and the status panel eases between states.
• .env-example pointed the relay at relay.5stack.gg, which doesn't exist; it's tv.5stack.gg.
• testDownload is added to the generated zeus types by hand; the next codegen after api#431 deploys produces the same.