fix: odkaz Otvorit v Brevo vedie priamo na upravu kampane (uloha 17)

Namiesto napevno zadaneho zoznamu kampani (404) sa odkaz sklada z ID
kampane: app.brevo.com/marketing-campaign/edit/{id}.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/brevo.ts

@@ -0,0 +1,4 @@
+// Priamy odkaz na úpravu konkrétnej kampane v Brevo
+export function getBrevoCampaignUrl(campaignId: number | string): string {
+  return `https://app.brevo.com/marketing-campaign/edit/${encodeURIComponent(String(campaignId))}`;
+}