Key changes from previous version:
- Remove overlay text from ns_ax_buffer_text (was causing spurious
'new line' announcements via VoiceOver text diff)
- Do NOT invalidate text cache on overlay change
- Two-reference face detection (handles selected at any position)
- SDATA scan instead of per-char Faref for newline detection
- Zoom tracking via UAZoomChangeFocus for selected candidate row
- Deduplication via cachedCompletionAnnouncement