feat: multi-user UI login with admin and monitor roles

Add sac_users table, JWT roles, settings/users API guarded for admin, Users page in UI, and sac_manage_user.py CLI.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/App.vue

@@ -8,11 +8,18 @@
 </template>
 
 <script setup lang="ts">
-import { computed } from "vue";
+import { computed, onMounted } from "vue";
 import { useRoute } from "vue-router";
 import { getToken } from "./api";
 import AppSidebar from "./components/AppSidebar.vue";
+import { refreshSessionRole } from "./router";
 
 const route = useRoute();
 const showShell = computed(() => route.path !== "/login" && !!getToken());
+
+onMounted(() => {
+  if (getToken()) {
+    void refreshSessionRole();
+  }
+});
 </script>