feat: add self-service account email changes

[jmgasper]

Summary

• Add a Change Email action beside Primary Email in Account Settings.
• Verify ownership with a six-digit OTP sent to the current email, then collect the proposed new address in a second modal.
• Send validation only to the new address and show a dedicated completion page before refreshing Account Settings.
• Keep the validation-link route available while logged out so login redirects cannot discard the signed token.
• Add a reusable accessible inline form-field action and focused API/route tests.

Service dependency

• feat: add secure self-service email change workflow identity-api-v6#45

Testing

• yarn lint
• yarn build
• yarn test:no-watch --runTestsByPath src/apps/accounts/src/accounts.routes.spec.tsx src/apps/accounts/src/lib/services/email-change.service.spec.ts --runInBand (2 tests)

The production build completes with the existing source-map, CSS-order, and bundle-size warnings.