feat: add contact-book variable registry for campaign personalization (#359)

* feat: add contact-book variable registry for campaign personalization

* test: include contact-book variables default in service expectation

* fix: address personalization review issues

* fix text

* fix: normalize contact variable access across contact flows

* stuff

* fix

apps/web/prisma/migrations/20260224120000_add_contact_book_variables/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "ContactBook" ADD COLUMN     "variables" TEXT[] NOT NULL DEFAULT ARRAY[]::TEXT[];