Add page builder admin UI + public page route (step 5 + step 6 client)

- PagesAdmin: list view of pages (title/slug/status/protected/updated) with
  new/edit navigation and a View link to the live page.
- PageBuilder: full-page block canvas — palette (adds any registered block),
  per-block editor cards with show/hide, up/down + native drag reorder, and
  remove; Content / Settings tabs; SEO metadata + layout/nav settings panels;
  publish/unpublish; protect (PATCH) and password-gated unprotect (modal);
  draft preview (mints a token, opens /preview/:id/:token); delete (blocked
  while protected). Surfaces server block-validation details on save.
- CmsPage: public renderer for /:slug (published; staff see drafts) and the
  token-gated /preview/:id/:token, rendering blocks via BlockList and
  reflecting the page title/meta.
- Routing: /:slug catch-all after all named routes + /preview/:id/:token
  outside the maintenance gate; admin /admin/pages, /pages/new, /pages/:id.
- api client: public page/pagePreview + admin pages CRUD/unprotect/preview.
- AdminLayout: "Pages" nav entry (Content group) with icon.
- theme.css: builder canvas + preview-banner + shell-wide styles.

Client builds clean (216 modules).

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

client/src/api/client.js

@@ -73,6 +73,10 @@ export const api = {
   wikiCategories: () => req('/public/wiki/categories'),
   wikiTags: () => req('/public/wiki/tags'),
   wikiPage: (slug) => req(`/public/wiki/${slug}`),
+  // CMS pages (block-based). Published-only for the public; a draft-preview link
+  // is fetched by id + token.
+  page: (slug) => req(`/public/pages/${slug}`),
+  pagePreview: (id, token) => req(`/public/pages/${id}/preview/${token}`),
   contact: (payload) => req('/public/contact', { method: 'POST', body: payload }),
 
   // ----- admin -----
@@ -97,6 +101,15 @@ export const api = {
       fd.append('image', file)
       return req('/admin/uploads', { method: 'POST', body: fd, raw: true })
     },
+    // ----- CMS pages (block-based page builder) -----
+    listPages: () => req('/admin/pages'),
+    getPage: (id) => req(`/admin/pages/${id}`),
+    createPage: (data) => req('/admin/pages', { method: 'POST', body: data }),
+    updatePage: (id, data) => req(`/admin/pages/${id}`, { method: 'PATCH', body: data }),
+    deletePage: (id) => req(`/admin/pages/${id}`, { method: 'DELETE' }),
+    unprotectPage: (id, password) =>
+      req(`/admin/pages/${id}/unprotect`, { method: 'POST', body: { password } }),
+    createPagePreview: (id) => req(`/admin/pages/${id}/preview`, { method: 'POST' }),
     listWiki: (params = '') => req(`/admin/wiki${params}`),
     getWiki: (slug) => req(`/admin/wiki/${slug}`),
     createWiki: (data) => req('/admin/wiki', { method: 'POST', body: data }),