chore: add an accessibility pass for the PWA

[DevSecNinja]

Why

Wazzup is a small personal app, but it should still be comfortable to use with keyboard navigation, screen readers, high contrast settings, and mobile assistive technologies.

Scope

• Review semantic structure, landmarks, heading order, focus states, and interactive card behavior.
• Check color contrast for muted text, tags, source/reference pills, and seen/new states.
• Verify keyboard flows for opening article cards, reference links, notification controls, and hide-seen controls.
• Add lightweight automated checks or browser-level assertions where they fit the project.

Acceptance criteria

• Main briefing interactions are usable by keyboard.
• Focus styles are visible and consistent.
• Common accessibility regressions have tests or documented manual checks.
• The UI stays visually aligned with the current design.