Add email change confirmation template and code link

[jmgasper]

Summary

• add a dedicated email-change confirmation HTML template using the actual userHandle and verificationAgreeUrl substitutions
• generate links for /account-settings/email-change/verify?code=...
• accept code on the public identity completion endpoint while retaining token for already-issued links
• document the email topic/template contract and updated environment URL

Deployment note

Create or update the SendGrid template from docs/email-templates/change-email-validation.html, then map member.action.email.profile.emailchange.verification to that template ID in the email service topic map.

Verification

• pnpm test --runInBand src/api/user/email-change.service.spec.ts src/api/user/email-change.controller.spec.ts
• pnpm lint
• pnpm build
• template substitution and retired-link validation script

Compatibility

Existing ?token=... API links and <emailChangeToken> URL configuration remain supported.

Related

• Account Settings route: Add account-settings email change confirmation route platform-ui#2208