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/routes/admin/AdminLayout.jsx

@@ -27,6 +27,7 @@ function Icon({ children, size = 16 }) {
 const IconHome = () => <Icon><path d="M3 10.5 12 3l9 7.5" /><path d="M5 9.5V21h14V9.5" /></Icon>
 const IconPosts = () => <Icon><path d="M5 3h14v18H5z" /><path d="M8 8h8M8 12h8M8 16h5" /></Icon>
 const IconWiki = () => <Icon><path d="M4 4h9a3 3 0 0 1 3 3v13a2 2 0 0 0-2-2H4z" /><path d="M20 4h-2a2 2 0 0 0-2 2v14a2 2 0 0 1 2-2h2z" /></Icon>
+const IconPages = () => <Icon><path d="M5 3h9l5 5v13H5z" /><path d="M14 3v5h5" /><path d="M8 13h8M8 17h8" /></Icon>
 const IconActivity = () => <Icon><path d="M3 12h4l3 8 4-16 3 8h4" /></Icon>
 const IconShield = () => <Icon><path d="M12 3l7 3v5c0 5-3.5 8-7 10-3.5-2-7-5-7-10V6z" /><path d="M9 12l2 2 4-4" /></Icon>
 const IconUsers = () => <Icon><circle cx="9" cy="8" r="3" /><path d="M3 20a6 6 0 0 1 12 0" /><path d="M16 6a3 3 0 0 1 0 6M17 20a6 6 0 0 0-3-5" /></Icon>
@@ -52,6 +53,7 @@ const NAV = [
     title: 'Content',
     items: [
       { to: '/admin/posts', label: 'Posts', icon: IconPosts, roles: ['admin', 'editor'] },
+      { to: '/admin/pages', label: 'Pages', icon: IconPages, roles: ['admin', 'editor'] },
       { to: '/admin/wiki', label: 'Wiki', icon: IconWiki, roles: ['admin', 'editor'] },
       { to: '/admin/activity', label: 'Activity', icon: IconActivity, roles: ['admin', 'editor'] },
     ],
@@ -85,6 +87,7 @@ const COLLAPSE_KEY = 'admin.nav.collapsed'
 const TITLES = {
   '/admin': 'Dashboard',
   '/admin/posts': 'Posts',
+  '/admin/pages': 'Pages',
   '/admin/wiki': 'Wiki Pages',
   '/admin/hero': 'Hero Editor',
   '/admin/moderation': 'Moderation',