a11y(admin): add polite live status announcements (#381)

[mysterio123865]

Summary

Implements Issue #381 by adding accessible live status announcements to the admin page. Status changes are announced politely without disrupting users, while avoiding unnecessary announcements on initial load or during rapid state changes.

Changes

• Added useAdminStatusAnnouncement hook

  • Provides debounced aria-live="polite" announcements
  • Announces Live, Paused, and Empty states
  • Suppresses announcements on initial mount and the first settled state
  • Coalesces rapid status updates into a single announcement

• Updated the admin page:

  • Added an sr-only live region with aria-live="polite"
  • Integrated the new announcement hook
  • Left existing pause/unpause behavior unchanged

Validation

• ✅ 100% statement coverage for useAdminStatusAnnouncement
• ✅ Admin page coverage ≥95%
• ✅ All admin tests passed (33)
• ✅ npm run build succeeded

Notes

• Full npm test still reports the existing api-keys test failures, which are unrelated to this change.
• Repository-wide lint continues to report pre-existing errors outside the admin module.
• Branch is up to date with upstream/main (1 commit ahead, 0 behind).

Closes #381

Commit

a11y(admin): announce updates politely