Add stealth mode to browser scraper and Ronis.hr store

- Switch puppeteer to puppeteer-extra with stealth plugin to
  bypass Cloudflare bot detection
- Add Ronis.hr store config (JS-rendered, 48 products per page)
- Stealth mode patches navigator.webdriver, chrome runtime, and
  other fingerprints that Cloudflare checks

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

stores/ronis-hr.yaml

@@ -0,0 +1,14 @@
+name: Ronis.hr
+base_url: https://www.ronis.hr
+search_url: https://www.ronis.hr/hr/rezultati-pretrage?s=1&keyword={query}
+category: Electronics
+currency: EUR
+render_js: true
+test_query: logitech
+
+selectors:
+  container: ".product-display-grid.item"
+  name: ".product-info h3"
+  price: ".product-price .price"
+  link: "a.product-display-grid-image"
+  image: ".image-wrapper img"