[focusgroup] Editorial fixes (#1380)

Editorial cleanup:
- Update date to reflect latest changes.
- Replace "*" with "-" for all list markers for consistency.
- Replace "&" with "and" in headings and prose.
- Fix heading level for Authoring guidance (### → ##) to match TOC.
- Add quotes around role attribute values (e.g., role="tabpanel").
- Remove trailing colon from heading.
- Remove consecutive blank lines.
- Preserve all substantive content from upstream (default modifiers,
  nowrap, button inference, etc.) while applying editorial fixes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: janewman