feat(nav): admin section label + role chip beside the user name

- A clearer 'Admin' section header (thicker centred rule when collapsed) above the
  admin-only modules (Scheduler/Configuration/Users), replacing the faint hairline.
- A small role chip (admin/user/demo) next to the account name — an avatar-corner dot
  when the rail is collapsed.

frontend/src/components/NavSidebar.tsx

@@ -171,6 +171,21 @@ export default function NavSidebar({
   const rowBase =
     "w-full flex items-center gap-3 rounded-lg px-2.5 py-2 text-sm transition";
   const name = me.display_name ?? me.email.split("@")[0];
+  // Role shown next to the name (expanded) / as an avatar dot (collapsed). Demo isn't a real
+  // role (it's a flag on a `user` row), so surface it first.
+  const roleKey: "admin" | "user" | "demo" = me.is_demo
+    ? "demo"
+    : me.role === "admin"
+      ? "admin"
+      : "user";
+  const roleChipCls =
+    roleKey === "admin"
+      ? "bg-accent/15 text-accent"
+      : roleKey === "demo"
+        ? "bg-amber-500/20 text-amber-500"
+        : "bg-muted/15 text-muted";
+  const roleDotCls =
+    roleKey === "admin" ? "bg-accent" : roleKey === "demo" ? "bg-amber-500" : "bg-muted";
 
   const renderItem = ({ page: p, icon: Icon, label, badge }: NavItem) => {
     const active = page === p;
@@ -247,9 +262,19 @@ export default function NavSidebar({
 
       <div className="flex-1 min-h-0 overflow-y-auto flex flex-col gap-1">
         {userItems.map(renderItem)}
-        {systemItems.length > 0 && (
-          <div className="my-1.5 border-t border-border/70" />
-        )}
+        {systemItems.length > 0 &&
+          (collapsed ? (
+            // Collapsed rail: a short, thicker centred rule is the clearest "new section" cue
+            // when there's no room for a label.
+            <div className="my-2 mx-auto w-7 border-t-2 border-border" />
+          ) : (
+            <div className="mt-4 mb-1 px-2.5 flex items-center gap-2">
+              <span className="text-[10px] font-semibold uppercase tracking-wider text-muted/70">
+                {t("nav.adminSection")}
+              </span>
+              <span className="flex-1 border-t border-border" />
+            </div>
+          ))}
         {systemItems.map(renderItem)}
       </div>
 
@@ -290,12 +315,27 @@ export default function NavSidebar({
             title={collapsed ? name : undefined}
             className={`${rowBase} ${collapsed ? "justify-center px-0" : ""} text-muted hover:text-fg hover:bg-card`}
           >
+            <span className="relative shrink-0">
               <AvatarImg
                 src={me.avatar_url}
                 fallback={name}
-              className="w-[22px] h-[22px] rounded-full text-[10px] shrink-0"
+                className="w-[22px] h-[22px] rounded-full text-[10px]"
               />
+              {collapsed && (
+                <span
+                  className={`absolute -bottom-0.5 -right-0.5 w-2.5 h-2.5 rounded-full ring-2 ring-bg ${roleDotCls}`}
+                  title={t(`nav.role.${roleKey}`)}
+                />
+              )}
+            </span>
             {!collapsed && <span className="truncate flex-1 text-left">{name}</span>}
+            {!collapsed && (
+              <span
+                className={`shrink-0 text-[10px] font-semibold uppercase tracking-wide px-1.5 py-0.5 rounded ${roleChipCls}`}
+              >
+                {t(`nav.role.${roleKey}`)}
+              </span>
+            )}
           </button>
 
           {acctOpen &&

frontend/src/i18n/locales/de/nav.json

@@ -1,5 +1,11 @@
 {
   "primary": "Hauptnavigation",
   "collapse": "Seitenleiste einklappen",
-  "expand": "Seitenleiste ausklappen"
+  "expand": "Seitenleiste ausklappen",
+  "adminSection": "Admin",
+  "role": {
+    "admin": "Admin",
+    "user": "Benutzer",
+    "demo": "Demo"
+  }
 }

frontend/src/i18n/locales/en/nav.json

@@ -1,5 +1,11 @@
 {
   "primary": "Primary navigation",
   "collapse": "Collapse sidebar",
-  "expand": "Expand sidebar"
+  "expand": "Expand sidebar",
+  "adminSection": "Admin",
+  "role": {
+    "admin": "Admin",
+    "user": "User",
+    "demo": "Demo"
+  }
 }

frontend/src/i18n/locales/hu/nav.json

@@ -1,5 +1,11 @@
 {
   "primary": "Fő navigáció",
   "collapse": "Oldalsáv összecsukása",
-  "expand": "Oldalsáv kinyitása"
+  "expand": "Oldalsáv kinyitása",
+  "adminSection": "Admin",
+  "role": {
+    "admin": "Admin",
+    "user": "Felhasználó",
+    "demo": "Demó"
+  }
 }