Sort roles

Visitors should be able to change the order of open roles to match how they browse. Add sorting for title and posted date while keeping the default newest-first experience.

Acceptance criteria

• The roles list can sort by title A–Z and Z–A.
• The roles list can sort by posted date newest and oldest.
• The sort control has a clear accessible label and stable data-testid.
• The selected sort order is reflected in the rendered role cards.
• Unit tests cover all sort modes.
• Playwright tests verify at least one title sort and one date sort.

Start at the roles list entry point and inspect the existing unit and Playwright test setup. Add title and posted-date sort modes while preserving newest-first as the default, with an accessible sort label and stable data-testid. Done means rendered role cards match every sort mode and tests cover all unit modes plus one title and one date sort in Playwright.