Migration helpers let the auth signUp flow transfer anonymous cookie consent
to an authenticated user's record. extractAnonymousConsent parses the raw
Cookie header; migrateAnonymousConsent calls IConsent.grant with
method: "signup-migration" for each granted category, making the migration
traceable in the audit log. No-op when the consent cookie is absent.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
