feat: add restart server action for vendor and tenant

Vendor: POST /api/vendor/tenants/{id}/restart (platform:admin scope)
Tenant: POST /api/tenant/server/restart (tenant:manage scope)

Both call TenantProvisioner.stop() then start() on the server + UI
containers. Restart button on vendor TenantDetailPage (Actions card)
and tenant TenantDashboardPage (Server card). Allowed in any status
including PROVISIONING.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/vendor/TenantDetailPage.tsx

@@ -16,6 +16,7 @@ import {
   useActivateTenant,
   useDeleteTenant,
   useRenewLicense,
+  useRestartServer,
 } from '../../api/vendor-hooks';
 import { ServerStatusBadge } from '../../components/ServerStatusBadge';
 import { tierColor } from '../../utils/tier';
@@ -67,6 +68,7 @@ export function TenantDetailPage() {
   const activateTenant = useActivateTenant();
   const deleteTenant = useDeleteTenant();
   const renewLicense = useRenewLicense();
+  const restartServer = useRestartServer();
 
   const [deleteOpen, setDeleteOpen] = useState(false);
 
@@ -105,6 +107,16 @@ export function TenantDetailPage() {
     }
   }
 
+  async function handleRestart() {
+    if (!id) return;
+    try {
+      await restartServer.mutateAsync(id);
+      toast({ title: 'Server restarted', variant: 'success' });
+    } catch (err) {
+      toast({ title: 'Restart failed', description: String(err), variant: 'error' });
+    }
+  }
+
   async function handleDelete() {
     if (!id) return;
     try {
@@ -247,6 +259,14 @@ export function TenantDetailPage() {
         {/* Actions */}
         <Card title="Actions">
           <div style={{ display: 'flex', flexDirection: 'column', gap: 10 }}>
+            <Button
+              variant="secondary"
+              onClick={handleRestart}
+              loading={restartServer.isPending}
+            >
+              <RefreshCw size={14} style={{ marginRight: 6 }} />
+              Restart Server
+            </Button>
             <Button
               variant="secondary"
               onClick={handleSuspendToggle}