Block saving a wizard-enabled onboarding schema with no fields

The "Enable verification wizard flow" checkbox and step/field editing
were decoupled with no validation tying them together — an admin could
toggle the wizard on and hit Save before adding any fields to a step,
instantly publishing a wizard with nothing to fill in. Save is now
disabled (with an inline message naming the empty step) until every
non-review step has at least one field. Mirrors the same check added
server-side in nxtgauge-backend-rust's create_onboarding_config.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/admin/OnboardingSchemaEditor.tsx

@@ -185,9 +185,25 @@ export default function OnboardingSchemaEditor() {
     );
   };
 
+  // Mirrors the backend check in create_onboarding_config — catches it before
+  // the round trip so an admin can't accidentally publish a wizard with
+  // nothing to fill in (checkbox on, but a step never got any fields added).
+  const validationError = (): string | null => {
+    if (!enableWizardFlow()) return null;
+    if (steps().length === 0) return 'Cannot enable the wizard flow with no steps configured.';
+    const emptyStep = steps().find((s) => s.type !== 'review' && s.fields.length === 0);
+    if (emptyStep) return `Cannot enable the wizard flow: step "${emptyStep.title || '(untitled step)'}" has no fields.`;
+    return null;
+  };
+
   const handleSave = async () => {
     const id = roleId();
     if (!id) return;
+    const error = validationError();
+    if (error) {
+      setMessage(error);
+      return;
+    }
     setSaving(true);
     setMessage('');
     try {
@@ -259,9 +275,10 @@ export default function OnboardingSchemaEditor() {
 
           <button
             type="button"
-            disabled={saving() || loading()}
+            disabled={saving() || loading() || !!validationError()}
             onClick={handleSave}
-            style={`height:36px;border-radius:8px;border:none;background:#0D0D2A;color:white;padding:0 16px;font-size:13px;font-weight:700;cursor:pointer;opacity:${saving() || loading() ? 0.6 : 1}`}
+            title={validationError() || undefined}
+            style={`height:36px;border-radius:8px;border:none;background:#0D0D2A;color:white;padding:0 16px;font-size:13px;font-weight:700;cursor:pointer;opacity:${saving() || loading() || validationError() ? 0.6 : 1}`}
           >
             {saving() ? 'Saving...' : 'Save Schema'}
           </button>