Implement multi-domain SEO improvements:

- Add metadata to login and login-verify pages to prevent indexing.
- Update robots.txt to disallow additional sensitive paths.
- Enhance sitemap generation to filter by city and include accurate last modified dates.
- Refactor canonical URL generation to support multi-domain architecture, ensuring self-canonicalization for city domains.
- Remove deprecated CanonicalHandler component and streamline canonical URL handling.
- Introduce safe JSON-LD output to prevent XSS vulnerabilities.
- Add payment layout with appropriate metadata to prevent indexing.
- Conduct a comprehensive technical SEO audit and implement necessary fixes across the application.

lib/sanitize.js

@@ -14,6 +14,11 @@ export function sanitizeHtml(html) {
   });
 }
 
+// خروجی امن برای <script type="application/ld+json"> — جلوگیری از بستن تگ با داده‌ی کاربر
+export function safeJsonLd(obj) {
+  return JSON.stringify(obj).replace(/</g, "\\u003c");
+}
+
 export function safeJsonParse(str, fallback = null) {
   if (!str) return fallback;
   try {