Add pages API: model, controller, routes, preview (steps 4/6/7/8)

Backend for the CMS page builder, all under the existing /api/v1:

- pages.model: authoritative save gate — validates blocks against the
  registry and sanitizes them on every create/update; maps rows to/from the
  grouped API shape (metadata / settings); slug validated + reserved-checked
  at create and immutable after; `protected` can be set true via PATCH but
  only cleared via the unprotect path; published_at stamped on first publish.
- sanitizeBlocks: post-validation normalizer (applies each block's sanitize,
  stamps version, defaults visible, recurses container slots).
- reservedSlugs: guards page slugs from shadowing named routes/API namespaces.
- Admin routes (staff-gated): GET/POST /pages, GET/PATCH/DELETE /pages/:id,
  POST /pages/:id/unprotect (password step-up, verified against the caller's
  own hash, never logged), POST /pages/:id/preview (1h token). Audit-logs
  create/publish/unpublish/protect/unprotect/delete.
- Public routes: GET /public/pages/:slug (published; staff see drafts; site-
  mode gated) and GET /public/pages/:id/preview/:token (ungated, token is the
  access control). Preview token primitives added to auth/token.js.
- Swagger annotations for all new endpoints.

Verified end-to-end: model integration test against the dev DB (sanitize,
invalid-block rejection, slug immutability, protected/unprotect, dup/reserved
slug, published_at) + authenticated HTTP smoke (201 create, 400 invalid
blocks, publish, public slug fetch, preview mint+fetch, 403 delete-protected,
401 wrong-password unprotect).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/model/pages/pages.db.js

@@ -0,0 +1,79 @@
+const { query } = require('../../utils/db')
+
+// `blocks` is stored as a JSON string (MEDIUMTEXT) and parsed in the model.
+const COLS = [
+  'id', 'slug', 'title', 'blocks', 'status', 'protected', 'author_id',
+  'seo_title', 'meta_description', 'og_image', 'canonical_url', 'robots',
+  'layout', 'show_in_nav', 'nav_group', 'nav_order',
+  'created_at', 'updated_at', 'published_at',
+].join(', ')
+
+// Admin list — every page, newest first. Excludes the (potentially large)
+// blocks payload; callers that need it fetch the row by id/slug.
+async function listSummaries() {
+  return query(
+    `SELECT id, slug, title, status, protected, show_in_nav, nav_group, nav_order,
+            updated_at, published_at
+     FROM pages ORDER BY updated_at DESC, id DESC`,
+  )
+}
+
+async function findById(id) {
+  const rows = await query(`SELECT ${COLS} FROM pages WHERE id = ? LIMIT 1`, [id])
+  return rows[0] || null
+}
+
+async function findBySlug(slug) {
+  const rows = await query(`SELECT ${COLS} FROM pages WHERE slug = ? LIMIT 1`, [slug])
+  return rows[0] || null
+}
+
+// Insert a fully-formed column map. `blocks` must already be a JSON string.
+async function insert(page) {
+  const res = await query(
+    `INSERT INTO pages
+      (slug, title, blocks, status, protected, author_id,
+       seo_title, meta_description, og_image, canonical_url, robots,
+       layout, show_in_nav, nav_group, nav_order, published_at)
+     VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+    [
+      page.slug,
+      page.title,
+      page.blocks,
+      page.status,
+      page.protected ? 1 : 0,
+      page.author_id ?? null,
+      page.seo_title ?? null,
+      page.meta_description ?? null,
+      page.og_image ?? null,
+      page.canonical_url ?? null,
+      page.robots ?? null,
+      page.layout ?? 'default',
+      page.show_in_nav ? 1 : 0,
+      page.nav_group ?? null,
+      page.nav_order ?? null,
+      page.published_at ?? null,
+    ],
+  )
+  return res.insertId
+}
+
+// Update only the provided columns. Keys must be real column names (the model
+// builds this map from a whitelist, never straight from the request body).
+async function update(id, fields) {
+  const cols = []
+  const params = []
+  for (const [key, val] of Object.entries(fields)) {
+    cols.push(`${key} = ?`)
+    params.push(val)
+  }
+  if (cols.length === 0) return
+  params.push(id)
+  await query(`UPDATE pages SET ${cols.join(', ')} WHERE id = ?`, params)
+}
+
+async function remove(id) {
+  return query('DELETE FROM pages WHERE id = ?', [id])
+}
+
+module.exports = { listSummaries, findById, findBySlug, insert, update, remove }