feat(engagement): templates — the email block family, renderer and seeded set (engagement Phase 5a)

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>

server/test/mailer.test.js

@@ -16,6 +16,7 @@ const assert = require('node:assert/strict')
 const nodemailer = require('nodemailer')
 const emailConfig = require('../src/model/emailConfig/emailConfig.model')
 const settings = require('../src/model/settings/settings.model')
+const templatesDb = require('../src/model/engagement/engagementTemplates.db')
 const mailer = require('../src/utils/mailer')
 const db = require('../src/utils/db')
 
@@ -41,6 +42,14 @@ beforeEach(() => {
   transportCfg = null
   emailConfig.recordStatus = async () => {}
   settings.get = async () => 'contact@example.com'
+  // Engagement Phase 5a: every body now comes from `engagement_templates`, so a
+  // send reaches three more model functions than it used to. Stubbed here for the
+  // reason everything else in this file is — the suite must never touch a database
+  // — and `getByKey` answering null exercises the shipped-seed fallback, which is
+  // exactly the state a fresh deployment is in before its first seed runs.
+  settings.getInstanceName = async () => 'UOMysticmoon'
+  settings.getShellBrand = async () => ({ logo: '', favicon: '', theme: null })
+  templatesDb.getByKey = async () => null
   nodemailer.createTransport = (cfg) => {
     transportCfg = cfg
     return { sendMail: async (opts) => { sent = opts; return { messageId: '1' } } }