refactor: reorganize package exports under namespaced paths

- Prefix feature exports with `features/` (auth, admin, provider)
- Prefix shared exports with `shared/` (components, icons, lib, config, logger, rate-limit)
- Add new explicit exports for `shared/logger`, `shared/config`, and `shared/rate-limit`
- Update internal imports to use package self-referencing (`@zen/core/shared/*`) instead of relative paths

src/features/admin/actions/statsActions.js

@@ -6,9 +6,9 @@
  *
  * ```javascript
  * // app/(admin)/admin/[...admin]/page.js
- * import { protectAdmin } from '@zen/core/admin';
- * import { getDashboardStats } from '@zen/core/admin/actions';
- * import { AdminPagesClient } from '@zen/core/admin/pages';
+ * import { protectAdmin } from '@zen/core/features/admin';
+ * import { getDashboardStats } from '@zen/core/features/admin/actions';
+ * import { AdminPagesClient } from '@zen/core/features/admin/pages';
  *
  * export default async function AdminPage({ params }) {
  *   const { user } = await protectAdmin();
@@ -30,7 +30,7 @@
 'use server';
 
 import { query } from '@zen/core/database';
-import { fail } from '../../../shared/lib/logger.js';
+import { fail } from '@zen/core/shared/logger';
 
 /**
  * Get total number of users