feat(rbac): Viewer-Rolle durchsetzen — alle Mutations nur für Admins

- middleware.go: RequireAdminForMutations() blockiert POST/PUT/DELETE
  für Nicht-Admins (GET/HEAD passieren immer durch)
- main.go: Middleware in den authed-Gruppe eingehängt — wirkt für
  alle ~30 Resource-Handler gleichzeitig
- api/client.ts: 403 → AntD-Notification "Nur Lesezugriff" statt
  stiller Fehler
- Header: "Nur lesen"-Badge + Tooltip wenn role=viewer
- i18n de+en: viewerBadge + viewerHint

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

management-ui/src/api/client.ts

@@ -1,4 +1,5 @@
 import axios, { type AxiosError } from 'axios'
+import { message } from 'antd'
 
 import { useAuthStore } from '../stores/auth'
 
@@ -38,6 +39,12 @@ apiClient.interceptors.response.use(
       window.location.replace('/login')
     }
 
+    // 403 admin_required → viewer account tried to mutate; show a
+    // one-time notification and let the calling mutation handle the rest.
+    if (error.response?.status === 403) {
+      message.error('Keine Berechtigung — dieser Account hat nur Lesezugriff.', 4)
+    }
+
     // 503 setup_required → kick to /setup so the wizard takes over.
     if (
       error.response?.status === 503 &&

management-ui/src/components/Layout/Header.tsx

@@ -1,5 +1,5 @@
-import { Button, Dropdown, Select, Space } from 'antd'
-import { GlobalOutlined, LogoutOutlined, MenuOutlined, UserOutlined } from '@ant-design/icons'
+import { Button, Dropdown, Select, Space, Tag, Tooltip } from 'antd'
+import { EyeOutlined, GlobalOutlined, LogoutOutlined, MenuOutlined, UserOutlined } from '@ant-design/icons'
 import { useNavigate } from 'react-router-dom'
 import { useTranslation } from 'react-i18next'
 
@@ -55,23 +55,32 @@ export default function Header({ pageTitle, onMenuToggle }: HeaderProps) {
           popupMatchSelectWidth={false}
         />
         {user && (
-          <Dropdown
-            menu={{
-              items: [
-                {
-                  key: 'logout',
-                  icon: <LogoutOutlined />,
-                  label: t('auth.logout'),
-                  onClick: onLogout,
-                },
-              ],
-            }}
-            placement="bottomRight"
-          >
-            <Button type="text" className="header-user">
-              <Space><UserOutlined />{user.actor}</Space>
-            </Button>
-          </Dropdown>
+          <>
+            {user.role === 'viewer' && (
+              <Tooltip title={t('auth.viewerHint')}>
+                <Tag icon={<EyeOutlined />} color="default" style={{ marginRight: 4 }}>
+                  {t('auth.viewerBadge')}
+                </Tag>
+              </Tooltip>
+            )}
+            <Dropdown
+              menu={{
+                items: [
+                  {
+                    key: 'logout',
+                    icon: <LogoutOutlined />,
+                    label: t('auth.logout'),
+                    onClick: onLogout,
+                  },
+                ],
+              }}
+              placement="bottomRight"
+            >
+              <Button type="text" className="header-user">
+                <Space><UserOutlined />{user.actor}</Space>
+              </Button>
+            </Dropdown>
+          </>
         )}
       </div>
     </header>

management-ui/src/i18n/locales/de/common.json

@@ -198,7 +198,9 @@
     "logout": "Abmelden",
     "loginFailed": "Anmeldung fehlgeschlagen",
     "loggedInAs": "Angemeldet als",
-    "forgotPassword": "Passwort vergessen?"
+    "forgotPassword": "Passwort vergessen?",
+    "viewerBadge": "Nur lesen",
+    "viewerHint": "Dieser Account hat die Rolle Betrachter — Änderungen sind gesperrt. Ein Admin kann die Rolle anpassen."
   },
   "reset": {
     "title": "Admin-Passwort zurücksetzen",

management-ui/src/i18n/locales/en/common.json

@@ -198,7 +198,9 @@
     "logout": "Sign out",
     "loginFailed": "Sign-in failed",
     "loggedInAs": "Signed in as",
-    "forgotPassword": "Forgot your password?"
+    "forgotPassword": "Forgot your password?",
+    "viewerBadge": "Read-only",
+    "viewerHint": "Your account has viewer role — all changes are blocked. Contact an admin to change your role."
   },
   "reset": {
     "title": "Reset admin password",