a11y(Login): announce the success Alert (check-email / reset-link-sent) to screen readers

[nastaso]

Context

On the auth form the error Alert is announced (role="alert" at src/pages/_Login.tsx line 363) but the success Alert one block below (line 369) has no role, so after a sign-up or "forgot password" submission the "check your email" / "reset link sent" confirmation is never announced. A non-sighted user gets no confirmation their action worked and may resubmit. (The reset-password and stats error alerts were handled in #53/#66; this is the Login success path they did not cover.)

Scope

• File: src/pages/_Login.tsx, the success <Alert tone="success"> (around line 369).
• Add role="status" (the correct polite-live role for a confirmation), mirroring the existing role="alert" on the error Alert.
• One-line markup change; no logic change.

Acceptance criteria

• The success Alert carries role="status".
• npm run lint and npm run test pass; no visual change.

[nastaso]

Resolved by #114: the Login success <Alert> now carries role="status" (assertive role="alert" stays on errors), so the check-email / reset-link confirmation is announced to screen readers. Closing as done.