Every subject and body moves out of `mailer.js` into `engagement_templates` rows an
operator can edit. A relocation, not a regression: nothing that sends mail today
starts depending on an operator authoring something first.
- `email.*` block family in its own registry, sharing the page family's envelope
walk and validate-then-sanitize order by binding rather than by copy.
- A server-side renderer producing both parts of a multipart message; the text
part is byte-identical to the literals this commit deletes.
- Nine seeded templates, six of them wired now; the seeder's `customized = 0`
guard lives in the UPDATE's own WHERE.
- `renderByKey` falls back to the shipped seed when a row is missing or unusable,
so no failure of the table can stop a password reset.
Also fixes `check:hosts` reading the template key `auth.email-verify` as the
hostname `auth.email`.
Co-Authored-By: Claude <noreply@anthropic.com>
