a11y: coverage reporting, WCAG AA audits, and keyboard navigation

[bobaivigitalpoint-ui]

Resolves #464
Resolves #465
Resolves #466
Resolves #467

Summary

#464 — Test coverage reporting integration

Added coverage reporting to frontend-ci.yml:

• New step runs npm run test:coverage (vitest v8/lcov, already configured in vitest.config.ts)
• Uploads lcov.info to Codecov (codecov/codecov-action@v4), informational only — no hard gate
• PR comment step posts a coverage summary (total line %) as an informational comment using actions/github-script

#465 — WCAG 2.1 AA audit for the send flow

• New frontend/tests/a11y/send-flow-audit.test.tsx runs axe-core against SendPageClient and BatchSendForm
• Shared helper frontend/tests/a11y/axe.ts wraps axe.run
• Audit documented in docs/A11Y_SEND_FLOW_AUDIT.md (automated + manual keyboard-only method, findings are triaged as follow-ups)

#466 — WCAG 2.1 AA audit for the claim flow

• New frontend/tests/a11y/claim-flow-audit.test.tsx runs axe-core against both the new-wallet (AccessibleClaimForm) and existing-wallet (ClaimStatusCard) paths
• Audit documented in docs/A11Y_CLAIM_FLOW_AUDIT.md including screen reader walkthrough notes

#467 — Keyboard navigation support across core flows

• Added visible :focus-visible outline (WCAG 2.1 AA 2.4.7) plus a skip-link pattern (2.4.1) to frontend/app/globals.css
• New frontend/tests/a11y/keyboard-navigation.test.tsx verifies the send mode toggle and claim form are fully completable with keyboard only (Tab/Enter/Space)

Also added axe-core dev dependency and a test:a11y script. No code was read/modified outside scope; changes are minimal and additive.

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