feat: enrich AgentInstanceResponse with version/capabilities, add password reset endpoint

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/api/queries/admin/rbac.ts

@@ -198,6 +198,19 @@ export function useDeleteUser() {
   });
 }
 
+export function useSetPassword() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async ({ userId, password }: { userId: string; password: string }) => {
+      await adminFetch(`/users/${userId}/password`, {
+        method: 'POST',
+        body: JSON.stringify({ password }),
+      });
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['admin', 'users'] }),
+  });
+}
+
 export function useAssignRoleToUser() {
   const qc = useQueryClient();
   return useMutation({