feat: create initial admin user + add vendor to new tenant orgs

When creating a tenant, the vendor can specify adminUsername +
adminPassword. The backend creates the user in Logto and assigns them
the owner org role. The vendor user is also auto-added to every new
org for support access.

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

ui/src/pages/vendor/CreateTenantPage.tsx

@@ -15,6 +15,8 @@ export function CreateTenantPage() {
   const [slug, setSlug] = useState('');
   const [slugTouched, setSlugTouched] = useState(false);
   const [tier, setTier] = useState('LOW');
+  const [adminUsername, setAdminUsername] = useState('');
+  const [adminPassword, setAdminPassword] = useState('');
 
   useEffect(() => {
     if (!slugTouched) {
@@ -25,7 +27,11 @@ export function CreateTenantPage() {
   async function handleSubmit(e: React.FormEvent) {
     e.preventDefault();
     try {
-      const result = await createTenant.mutateAsync({ name, slug, tier });
+      const result = await createTenant.mutateAsync({
+        name, slug, tier,
+        adminUsername: adminUsername || undefined,
+        adminPassword: adminPassword || undefined,
+      });
       toast({ title: 'Tenant created', variant: 'success' });
       navigate(`/vendor/tenants/${result.id}`);
     } catch (err) {
@@ -85,6 +91,25 @@ export function CreateTenantPage() {
             </select>
           </FormField>
 
+          <FormField label="Admin Username" htmlFor="admin-user" hint="Initial tenant admin (owner role)">
+            <Input
+              id="admin-user"
+              value={adminUsername}
+              onChange={(e) => setAdminUsername(e.target.value)}
+              placeholder="admin"
+            />
+          </FormField>
+
+          <FormField label="Admin Password" htmlFor="admin-pass">
+            <Input
+              id="admin-pass"
+              type="password"
+              value={adminPassword}
+              onChange={(e) => setAdminPassword(e.target.value)}
+              placeholder="••••••••"
+            />
+          </FormField>
+
           <div style={{ display: 'flex', gap: 8, justifyContent: 'flex-end', paddingTop: 8 }}>
             <Button
               type="button"

ui/src/types/api.ts

@@ -55,6 +55,8 @@ export interface CreateTenantRequest {
   name: string;
   slug: string;
   tier?: string;
+  adminUsername?: string;
+  adminPassword?: string;
 }
 
 // Tenant portal API types