refactor: remove redundant role field, keep only is_admin

- Remove role column from users schema (migration 0003)
- Update auth and admin services to use is_admin only
- Remove role from JWT token payloads
- Update admin CLI to use is_admin field
- Update frontend admin page to use isAdmin boolean
- Fix security: remove console.log dumping credentials in settings

Co-Authored-By: Claude <noreply@anthropic.com>

drizzle/0003_tired_warpath.sql

@@ -0,0 +1 @@
+ALTER TABLE `users` DROP COLUMN `role`;