feat: Add 19 free QR code tools with SEO optimization

- Added PayPal, Zoom, Teams QR generators
- Added lazy loading for html-to-image (performance)
- Created 19 OG images for social sharing
- Added robots.txt and updated sitemap
- Fixed mobile navigation with accordion menu
- Added 7 color options per generator
- Fixed crypto QR with universal/wallet mode toggle
- Hero QR codes all point to qrmaster.net

public/robots.txt

@@ -0,0 +1,19 @@
+# QR Master - robots.txt
+# Allow all search engines to crawl all pages
+
+User-agent: *
+Allow: /
+
+# Sitemap location
+Sitemap: https://www.qrmaster.net/sitemap.xml
+
+# Crawl-delay (optional, be nice to servers)
+Crawl-delay: 1
+
+# Disallow admin/api routes
+Disallow: /api/
+Disallow: /dashboard/
+Disallow: /_next/
+
+# Allow all free tools explicitly
+Allow: /tools/