refactor: remove module system integration from admin and CLI

Removes all module-related logic from the admin dashboard, CLI database
initialization, and AdminPages component:

- Drop `initModules` call from `db init` CLI command and simplify the
  completion message to only reflect core feature tables
- Remove `getModuleDashboardStats` and module page routing from admin
  stats actions and update usage documentation accordingly
- Simplify `AdminPagesClient` to remove module page loading, lazy
  components, and module-specific props (`moduleStats`, `modulePageInfo`,
  `routeInfo`, `enabledModules`)

src/features/admin/actions/statsActions.js

@@ -1,34 +1,26 @@
 /**
  * Admin Stats Actions
  * Server-side actions for core dashboard statistics
- * 
- * Module-specific stats are handled by each module's dashboard actions.
- * See src/modules/{module}/dashboard/statsActions.js
- * 
+ *
  * Usage in your Next.js app:
- * 
+ *
  * ```javascript
  * // app/(admin)/admin/[...admin]/page.js
  * import { protectAdmin } from '@zen/core/admin';
- * import { getDashboardStats, getModuleDashboardStats } from '@zen/core/admin/actions';
+ * import { getDashboardStats } from '@zen/core/admin/actions';
  * import { AdminPagesClient } from '@zen/core/admin/pages';
- * 
+ *
  * export default async function AdminPage({ params }) {
  *   const { user } = await protectAdmin();
- *   
- *   // Fetch core dashboard stats
+ *
  *   const statsResult = await getDashboardStats();
  *   const dashboardStats = statsResult.success ? statsResult.stats : null;
- *   
- *   // Fetch module dashboard stats (for dynamic widgets)
- *   const moduleStats = await getModuleDashboardStats();
- *   
+ *
  *   return (
- *     <AdminPagesClient 
- *       params={params} 
+ *     <AdminPagesClient
+ *       params={params}
  *       user={user}
  *       dashboardStats={dashboardStats}
- *       moduleStats={moduleStats}
  *     />
  *   );
  * }
@@ -72,9 +64,9 @@ export async function getDashboardStats() {
     };
   } catch (error) {
     fail(`Error getting dashboard stats: ${error.message}`);
-    return { 
-      success: false, 
-      error: error.message || 'Failed to get dashboard statistics' 
+    return {
+      success: false,
+      error: error.message || 'Failed to get dashboard statistics'
     };
   }
 }