Detect updates without browser refresh

[olegberman]

What changed

• Hide the update banner and duplicate install action after the Cloudflare build starts.
• Recheck the signed stable release on sign-in, foreground return, and a bounded interval.
• Accelerate service-worker checks during an active update and retain the build marker across a same-tab refresh.
• Publish the change as HQBase 0.1.20 with release notes.
• Update staging coverage to assert foreground detection without page.reload().

Why

Update availability was held in stale component state, the shell checked only every six hours, and starting a build did not inform the PWA lifecycle.

Validation

• CI=true pnpm check
• CI=true pnpm deploy:dry-run
• Rendered at 1280x720 and 390x844