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/auth/db.js

@@ -4,7 +4,7 @@
  */
 
 import { query, tableExists } from '@zen/core/database';
-import { done, warn } from '../../shared/lib/logger.js';
+import { done, warn } from '@zen/core/shared/logger';
 
 const AUTH_TABLES = [
   {