core: implement accessibility (WCAG 2.1 AA compliance)

[EmeditWeb]

Problem

The web app has no accessibility considerations.
Screen readers cannot navigate. Keyboard navigation
does not work.

What To Build

1. Semantic HTML audit
2. Keyboard navigation (tab order, focus styles)
3. Screen reader support (aria attributes)
4. Color contrast compliance (4.5:1 ratio)
5. Form accessibility (labels, error messages)
6. axe-core CI integration

Files To Touch

All component files in src/components/
All page files in src/pages/

Acceptance Criteria

• axe-core reports zero violations
• Keyboard navigation works on all pages
• Screen reader can complete main flows
• Color contrast meets WCAG AA
• npm run build passes

Mandatory Checks Before PR

• npm run build passes
• axe-core scan passes
• PR references this issue

[Adeyemi-cmd]

i would love to work on this