## Why

The site needs a more robust, state-of-the-art UX baseline: a minimum standard of WCAG 2.2 AA accessibility and a consistently responsive UI across devices and large displays.

## What Changes

- Establish a minimum accessibility baseline targeting WCAG 2.2 AA (without aiming for perfect/100% compliance).
- Make the UI fully responsive across common breakpoints (mobile/tablet/desktop/large desktop).
- Update the primary navigation to collapse into a hamburger menu on smaller viewports with mild animation.
- Fix the background gradient so it does not show abrupt cuts/banding at larger resolutions.
- Introduce a smoother, display-friendly font stack (and apply it consistently).

## Capabilities

### New Capabilities

- `wcag-responsive-ui`: Accessibility + responsive UI shell standards for layout, navigation, typography, and global styling (WCAG 2.2 AA baseline).

### Modified Capabilities

<!-- None expected; this change introduces a new UI-shell capability that affects multiple pages/components. -->

## Impact

- Frontend UI: `site/src/layouts/*`, header/navigation components, shared UI components, and global CSS (`site/public/styles/global.css`).
- Interaction patterns: keyboard navigation and focus styles, menu toggle behavior, and motion controls (respecting reduced-motion preferences).
- Visual design: typography and background rendering across large screens.
- Verification: add/update checks/tests for responsive nav behavior and basic accessibility expectations (e.g., menu toggle labeling, focus visibility).