docs: align getting-started tables with passkey-authentication.md style

- Scopes & Claims: one-claim-per-row with Example Value and Description columns
- ACR table: HTML with icon headers, lightbulb icons, legend, Remarks column
- AMR table: same icon-based format with Remarks for phr/hwk
- Add shared CSS (acr-table, amr-table, icon-legend, table-scroll)

Author: phaupt