Paginate roles

Long role lists are easier to scan when candidates can move through manageable pages. Add pagination for the roles list while keeping navigation accessible.

Acceptance criteria

• The roles list renders a configurable number of roles per page.
• Pagination helpers in src/lib/ operate on plain Job[] data.
• Previous and next controls have accessible names, disabled states, and stable data-testid attributes.
• Pagination works with empty and single-page lists.
• Unit tests cover pagination helpers and edge cases.
• Playwright tests cover moving between pages.

Locate the roles-list entry point and the pagination helpers under src/lib/, then inspect the existing unit and Playwright test setup. Implement configurable page sizing, accessible previous and next controls, and empty or single-page handling. Done means the helper edge cases and moving between pages are covered by the requested unit and Playwright tests.