feat: export a import kampani a cenoviek pre prenos na novy server

- npm run db:export: kampane a sablony cenoviek do supabase/data/ (+ obrazky z uloziska)
- npm run db:import [-- --dry-run]: nahra data s povodnymi ID, prepise odkazy
  na nove ulozisko, da sa spustit opakovane
- aktualny export: 7 kampani, 1 sablona cenovky

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

supabase/data/meta.json

@@ -0,0 +1,4 @@
+{
+  "exportedAt": "2026-10-19T08:59:25.680Z",
+  "sourceStorageBase": "https://dqexxfspkylqttrtxsww.supabase.co/storage/v1/object/public/newsletter-assets/"
+}