Security hardening + new tools deployment

- Hide Apache version (ServerTokens Prod)
- Add Permissions-Policy header
- Remove deprecated X-XSS-Protection
- Consolidate security headers to .htaccess only (remove duplicates from PHP)
- Deploy free tools: robots-analyzer, data-converter
- Deploy tools announcement blog post
- Update sitemap with new tools and blog post

includes/footer.php

@@ -33,6 +33,7 @@
             <div class="footer-section">
                 <h3>Resources & Insights</h3>
                 <ul>
+                    <li><a href="/tools/">Free Tools</a></li>
                     <li><a href="/blog/">Data Intelligence Blog</a></li>
                     <li><a href="/case-studies/">Case Studies</a></li>
                     <li><a href="/about">About UK Data Services</a></li>