fix: decouple at-rest encryption from JWT_SECRET, add JWT rotation

Introduces a dedicated ENCRYPTION_KEY for encrypting stored secrets
(API keys, MFA TOTP, SMTP password, OIDC client secret) so that
rotating the JWT signing secret no longer invalidates encrypted data,
and a compromised JWT_SECRET no longer exposes stored credentials.

- server/src/config.ts: add ENCRYPTION_KEY (auto-generated to
  data/.encryption_key if not set, same pattern as JWT_SECRET);
  switch JWT_SECRET to `export let` so updateJwtSecret() keeps the
  CJS module binding live for all importers without restart
- apiKeyCrypto.ts, mfaCrypto.ts: derive encryption keys from
  ENCRYPTION_KEY instead of JWT_SECRET
- admin POST /rotate-jwt-secret: generates a new 32-byte hex secret,
  persists it to data/.jwt_secret, updates the live in-process binding
  via updateJwtSecret(), and writes an audit log entry
- Admin panel (Settings → Danger Zone): "Rotate JWT Secret" button
  with a confirmation modal warning that all sessions will be
  invalidated; on success the acting admin is logged out immediately
- docker-compose.yml, .env.example, README, Helm chart (values.yaml,
  secret.yaml, deployment.yaml, NOTES.txt, README): document
  ENCRYPTION_KEY and its upgrade migration path

client/src/api/client.ts

@@ -185,6 +185,7 @@ export const adminApi = {
   deleteMcpToken: (id: number) => apiClient.delete(`/admin/mcp-tokens/${id}`).then(r => r.data),
   getPermissions: () => apiClient.get('/admin/permissions').then(r => r.data),
   updatePermissions: (permissions: Record<string, string>) => apiClient.put('/admin/permissions', { permissions }).then(r => r.data),
+  rotateJwtSecret: () => apiClient.post('/admin/rotate-jwt-secret').then(r => r.data),
 }
 
 export const addonsApi = {

client/src/pages/AdminPage.tsx

@@ -16,7 +16,7 @@ import PackingTemplateManager from '../components/Admin/PackingTemplateManager'
 import AuditLogPanel from '../components/Admin/AuditLogPanel'
 import AdminMcpTokensPanel from '../components/Admin/AdminMcpTokensPanel'
 import PermissionsPanel from '../components/Admin/PermissionsPanel'
-import { Users, Map, Briefcase, Shield, Trash2, Edit2, Camera, FileText, Eye, EyeOff, Save, CheckCircle, XCircle, Loader2, UserPlus, ArrowUpCircle, ExternalLink, Download, GitBranch, Sun, Link2, Copy, Plus } from 'lucide-react'
+import { Users, Map, Briefcase, Shield, Trash2, Edit2, Camera, FileText, Eye, EyeOff, Save, CheckCircle, XCircle, Loader2, UserPlus, ArrowUpCircle, ExternalLink, Download, GitBranch, Sun, Link2, Copy, Plus, RefreshCw, AlertTriangle } from 'lucide-react'
 import CustomSelect from '../components/shared/CustomSelect'
 
 interface AdminUser {
@@ -123,10 +123,13 @@ export default function AdminPage(): React.ReactElement {
   const [updateInfo, setUpdateInfo] = useState<UpdateInfo | null>(null)
   const [showUpdateModal, setShowUpdateModal] = useState<boolean>(false)
 
-  const { user: currentUser, updateApiKeys, setAppRequireMfa, setTripRemindersEnabled } = useAuthStore()
+  const { user: currentUser, updateApiKeys, setAppRequireMfa, setTripRemindersEnabled, logout } = useAuthStore()
   const navigate = useNavigate()
   const toast = useToast()
 
+  const [showRotateJwtModal, setShowRotateJwtModal] = useState<boolean>(false)
+  const [rotatingJwt, setRotatingJwt] = useState<boolean>(false)
+
   useEffect(() => {
     loadData()
     loadAppConfig()
@@ -1132,6 +1135,31 @@ export default function AdminPage(): React.ReactElement {
                   </div>
                 </div>
               </div>
+
+              {/* Danger Zone */}
+              <div className="bg-white rounded-xl border border-red-200 overflow-hidden">
+                <div className="px-6 py-4 border-b border-red-100 bg-red-50">
+                  <h2 className="font-semibold text-red-700 flex items-center gap-2">
+                    <AlertTriangle className="w-4 h-4" />
+                    Danger Zone
+                  </h2>
+                </div>
+                <div className="p-6">
+                  <div className="flex items-center justify-between">
+                    <div>
+                      <p className="text-sm font-medium text-slate-700">Rotate JWT Secret</p>
+                      <p className="text-xs text-slate-400 mt-0.5">Generate a new JWT signing secret. All active sessions will be invalidated immediately.</p>
+                    </div>
+                    <button
+                      onClick={() => setShowRotateJwtModal(true)}
+                      className="flex items-center gap-2 px-4 py-2 bg-red-600 hover:bg-red-700 text-white rounded-lg text-sm font-medium transition-colors"
+                    >
+                      <RefreshCw className="w-4 h-4" />
+                      Rotate
+                    </button>
+                  </div>
+                </div>
+              </div>
             </div>
           )}
 
@@ -1361,6 +1389,54 @@ docker run -d --name nomad \\
           </div>
         </div>
       )}
+
+      {/* Rotate JWT Secret confirmation modal */}
+      <Modal
+        isOpen={showRotateJwtModal}
+        onClose={() => setShowRotateJwtModal(false)}
+        title="Rotate JWT Secret"
+        size="sm"
+        footer={
+          <div className="flex gap-3 justify-end">
+            <button
+              onClick={() => setShowRotateJwtModal(false)}
+              disabled={rotatingJwt}
+              className="px-4 py-2 text-sm text-slate-600 border border-slate-200 rounded-lg hover:bg-slate-50 disabled:opacity-50"
+            >
+              {t('common.cancel')}
+            </button>
+            <button
+              onClick={async () => {
+                setRotatingJwt(true)
+                try {
+                  await adminApi.rotateJwtSecret()
+                  setShowRotateJwtModal(false)
+                  logout()
+                  navigate('/login')
+                } catch {
+                  toast.error(t('common.error'))
+                  setRotatingJwt(false)
+                }
+              }}
+              disabled={rotatingJwt}
+              className="flex items-center gap-2 px-4 py-2 text-sm bg-red-600 hover:bg-red-700 disabled:bg-red-300 text-white rounded-lg font-medium"
+            >
+              {rotatingJwt ? <div className="w-4 h-4 border-2 border-white/30 border-t-white rounded-full animate-spin" /> : <RefreshCw className="w-4 h-4" />}
+              Rotate &amp; Log out
+            </button>
+          </div>
+        }
+      >
+        <div className="flex gap-3">
+          <div className="flex-shrink-0 w-10 h-10 rounded-full bg-red-100 flex items-center justify-center">
+            <AlertTriangle className="w-5 h-5 text-red-600" />
+          </div>
+          <div>
+            <p className="text-sm font-medium text-slate-900 mb-1">Warning, this will invalidate all sessions and log you out.</p>
+            <p className="text-xs text-slate-500">A new JWT secret will be generated immediately. Every logged-in user — including you — will be signed out and will need to log in again.</p>
+          </div>
+        </div>
+      </Modal>
     </div>
   )
 }