Function announce

announce(message: string, priority?: "polite" | "assertive"): void
Announce a message to screen readers via an ARIA live region.

Clears the region first and sets content after a short delay to force re-announcement of identical messages.
Parameters
- message: string
  The text to announce
- priority: "polite" | "assertive" = 'polite'
  'polite' for non-urgent, 'assertive' for immediate
Returns void
- Defined in shared/accessibility/aria_live.ts:47