chore: zalozenie databazy a uloziska na novom serveri

- supabase/schema.sql: idempotentny skript (tabulky, RLS, bucket newsletter-assets)
- supabase/assets + npm run db:upload-assets: staticke obrazky sablony
- adresa uloziska sa sklada z NEXT_PUBLIC_SUPABASE_URL namiesto pevneho projektu
- .env.example a navod na instalaciu v README

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

scripts/upload-assets.mjs

@@ -0,0 +1,45 @@
+// Nahrá statické obrázky aplikácie (supabase/assets/) do Supabase Storage bucketu newsletter-assets.
+// Spustenie: npm run db:upload-assets   (číta NEXT_PUBLIC_SUPABASE_URL a SUPABASE_SERVICE_ROLE_KEY z .env.local)
+// Existujúce súbory s rovnakým názvom sa prepíšu.
+import { createClient } from '@supabase/supabase-js';
+import { readdir, readFile } from 'node:fs/promises';
+import path from 'node:path';
+
+const BUCKET = 'newsletter-assets';
+const ASSETS_DIR = path.join(process.cwd(), 'supabase', 'assets');
+const CONTENT_TYPES = {
+  '.png': 'image/png',
+  '.jpg': 'image/jpeg',
+  '.jpeg': 'image/jpeg',
+  '.gif': 'image/gif',
+  '.svg': 'image/svg+xml',
+  '.webp': 'image/webp'
+};
+
+const url = process.env.NEXT_PUBLIC_SUPABASE_URL;
+const serviceKey = process.env.SUPABASE_SERVICE_ROLE_KEY;
+if (!url || !serviceKey) {
+  console.error('Chýba NEXT_PUBLIC_SUPABASE_URL alebo SUPABASE_SERVICE_ROLE_KEY v .env.local');
+  process.exit(1);
+}
+
+const supabase = createClient(url, serviceKey);
+const files = (await readdir(ASSETS_DIR)).filter((f) => CONTENT_TYPES[path.extname(f).toLowerCase()]);
+
+let failed = 0;
+for (const file of files) {
+  const body = await readFile(path.join(ASSETS_DIR, file));
+  const { error } = await supabase.storage.from(BUCKET).upload(file, body, {
+    contentType: CONTENT_TYPES[path.extname(file).toLowerCase()],
+    upsert: true
+  });
+  if (error) {
+    failed++;
+    console.error(`✗ ${file}: ${error.message}`);
+  } else {
+    console.log(`✓ ${file}`);
+  }
+}
+
+console.log(`\nNahraté ${files.length - failed}/${files.length} súborov do bucketu ${BUCKET}.`);
+if (failed) process.exit(1);