Announce onboarding async errors to screen readers

[Abidoyesimze]

Summary

connectionError in WalletConnectStep and depositError in FirstDepositStep render failure text in a plain div with no role="alert"/aria-live. A screen-reader user who hits an async failure gets no notification.

Affected files

• src/components/onboarding/steps/WalletConnectStep.tsx
• src/components/onboarding/steps/FirstDepositStep.tsx

Tasks

• Add role="alert" (or aria-live="assertive") to both error containers.
• Verify a screen reader announces the error text when it appears.

Acceptance criteria

• Scope is limited to the files listed (or agreed alternatives in the PR).
• Change is verifiable: tests, screenshots, or written QA steps in the PR.
• No behavior regressions in related user flows.
• No new duplicate abstractions without a one-line rationale in the PR.

Suggested labels

a11y, onboarding

Notes

Sourced from the 2026-07-25 round-2 follow-up audit of the frontend codebase at commit 779e531, run after the first 60-issue audit batch (#525-#584) was substantially resolved. Verified against current file content at time of writing.