feat: add visual page builder to God Mode

- ContentLibrary component with blocks/avatars/fragments tabs
- EnhancedPageBuilder wrapper integrating visual editor
- Template library with funnel templates
- Avatar variable injection utility
- Builder route at /admin/pages/builder/[id]

Ready for page creation with visual editing.

src/pages/admin/pages/builder/[id].astro

@@ -0,0 +1,15 @@
+---
+import AdminLayout from '@/layouts/AdminLayout.astro';
+import { EnhancedPageBuilder } from '@/components/admin/pages/EnhancedPageBuilder';
+
+const { id } = Astro.params;
+const siteId = Astro.url.searchParams.get('site') || '';
+---
+
+<AdminLayout title="Page Builder">
+  <EnhancedPageBuilder 
+    pageId={id === 'new' ? undefined : id}
+    siteId={siteId}
+    client:only="react"
+  />
+</AdminLayout>