a11y: audit website and dashboard accessibility

[TFT444]

Goal

Complete an evidence-based accessibility audit for the OpenShield website and dashboard, supporting OpenSSF Silver tracker #199.

Scope

• Keyboard navigation and visible focus
• Semantic headings, landmarks, labels, and buttons
• Image and icon text alternatives
• Colour contrast and non-colour status indicators
• Responsive zoom/reflow and reduced motion
• Automated accessibility checks plus manual keyboard review

Completion

• Audit findings are documented by page/component
• Critical and high-impact barriers are fixed
• Accessibility checks run in CI where practical
• Manual keyboard testing is recorded
• Public documentation accurately states the achieved level
• Silver evidence register is updated

[TFT444]

Implementation is ready in #206. Accessibility source checks, semantic navigation/dialog/status improvements, keyboard skip navigation, and the audit document are included. All CI and security checks pass.