fix(a11y): single-select pill groups across the site show the choice only by colour #1069

Follow-up to #1067, from a site-wide scan of live rate.vn: button groups where one pill is styled as selected but no button carries aria-pressed, aria-selected or aria-current (WCAG 1.3.1 and 4.1.2).

• Product page:
  • price-history store filter and time range (30 days / 90 days / all);
  • total-cost calculator months;
  • trade-in options.
• Compare: weight presets ("Cân bằng" and the others).
• /deals: category filter.
• /merchants: platform filter and review-risk filter.
• /developers: endpoint list and code-language switcher.

The merchant profile's export row (copy summary, CSV, ...) is a set of actions, not a selection, and is out of scope.

Fix: name each group (role="group" with a visible heading or an aria-label) and give its buttons aria-pressed. The developers code switcher may use the full tabs pattern if it has panels.

Acceptance: a scan of these pages finds no single-select button group without exposed state. E2E covers one group per page.