Add live region announcements and an a11y pass to the SettlementModal processing states

[1nonlypiece]

📌 Description

src/components/modals/SettlementModal.tsx transitions through
eligible → processing → settled/error with per-step states (initiating,
confirming, finalizing), but status changes are conveyed visually only.
Screen-reader users do not hear progress, and the ineligible-reason copy needs
verified accessible association.

This issue adds ARIA live-region announcements for state/step changes and audits
the modal's accessibility (focus, labelling, escape) without changing its visual
design.

🎯 Requirements and Context

• Announce state and processing-step changes via a polite live region.
• Ensure the dialog has proper role, label, focus trap, and escape handling.
• Verify ineligible-reason category copy is associated and announced.
• No visual regressions to existing states.

🛠️ Suggested Execution

1. Fork the repo and create a branch

git checkout -b a11y/settlement-modal-live-regions

2. Implement changes

• Update src/components/modals/SettlementModal.tsx with a live region and any
  ARIA/focus fixes.
• Add src/components/modals/SettlementModal.a11y.test.tsx covering announcements
  on each transition, focus trap, escape, and reason-copy association.
• Add docs/accessibility/SETTLEMENT_MODAL_A11Y.md documenting the behaviour.
• Validate with keyboard-only and screen-reader expectations.

3. Test and commit

• Run pnpm test.
• Cover edge cases: rapid state changes, processing→error, ineligible categories,
  escape during processing.

Example commit message

a11y: live-region announcements for SettlementModal states

✅ Guidelines

• Minimum 95% test coverage on changed lines.
• Clear, reviewer-friendly documentation.
• Timeframe: 96 hours.

🏷️ Labels

type-security · type-enhancement · area-frontend · MAYBE REWARDED ·
GRANTFOX OSS · OFFICIAL CAMPAIGN

💬 Community & Support

• Join the CommitLabs contributor Discord to coordinate and get unblocked fast:
  https://discord.gg/WV7tdYkJk
• Introduce yourself before starting so we can avoid duplicate work and pair you
  with a reviewer. Maintainers triage actively and review fast.

[smog123]

@smog123 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'd like to work on this issue. I can add ARIA live-region announcements for settlement state and step transitions (eligible → processing → settled/error, including initiating/confirming/finalizing), and ensure screen readers receive clear updates without changing the visual design. I’ll also audit and fix modal accessibility (proper dialog role, labeling, focus trap, and escape handling) and ensure ineligible-reason copy is correctly associated and announced for assistive technologies.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @smog123 to this issue.

[GBOYEE]

I'd like to work on this.

Approach:

• I'll analyze the codebase and implement a clean solution
• Verify with existing tests + add new ones if needed

Estimated effort: ~1-2 hours. PR incoming shortly.

[GBOYEE]

I'd like to work on this.

Approach:

• I'll analyze the codebase and implement a clean solution
• Verify with existing tests + add new ones if needed

Estimated effort: ~1-2 hours. PR incoming shortly.

[GBOYEE]

I'd like to work on this.

Approach:

• Read the relevant codebase and understand the scope
• Implement the changes with clean, tested code
• Verify with existing tests + add new ones

Estimated effort: ~1-2 hours. PR incoming shortly. Closes #662