fix(a11y): leaderboard and compare selectors expose no selected state #1067

Found in a live keyboard and ARIA audit of rate.vn (round 5).

• Category switchers on /leaderboard and the compare pages use role="tablist"/role="tab", but there is no tabpanel and no aria-controls, the arrow keys do not move between tabs, and every tab is in the tab order. Screen readers announce tabs whose keyboard behaviour does not match. They are single-select filters over the whole page, not tabs with panels.
• Leaderboard pill groups (ranking criterion, use-case persona, price segment) show the selected pill only by colour. No aria-pressed and no group label (WCAG 1.3.1 and 4.1.2).
• The "customize weights" button shows and hides the slider panel without aria-expanded.

Fix:

• Make each selector a role="group" with an accessible name, and give its buttons aria-pressed.
• Give the customize button aria-expanded and aria-controls.

Acceptance: no role="tab" without the full pattern. Every selector group is named and exposes its pressed button. E2E covers the leaderboard and compare.