feat: submit visitor_id with nomination form

Include the persistent OpenPanel visitor UUID (from localStorage) in
the nomination payload for attribution tracking.

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

Author: vinogradovkonst

src/components/NominationForm.tsx

@@ -104,6 +104,7 @@ export default function NominationForm() {
                 website: hpField?.value || undefined,
                 turnstile_token: token,
                 form_loaded_at: formLoadedAt.current,
+                visitor_id: (window as any).__oseVisitorId || undefined,
             };
 
             try {