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/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1768988121232,
       "tag": "0002_nervous_layla_miller",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "6",
+      "when": 1768989260562,
+      "tag": "0003_tired_warpath",
+      "breakpoints": true
     }
   ]
 }