Fix navbar across all pages: add nav include, fonts, active state, spacing, stats, error pages

- Add nav.php include to 5 missing pages (cost-calculator, thank-you, 403, 404, 500)
- Add ErrorDocument directives to .htaccess for custom 403/404/500 pages
- Fix bogus accuracy stats (homepage, web-scraping, location pages)
- Fix invisible CTA buttons on property and financial service pages
- Add Google Fonts (Roboto Slab + Lato) to all pages missing it (tools, blog articles, error pages)
- Add active nav link highlighting (teal underline for current page)
- Improve footer contrast to WCAG AA, equal-height cards, mobile text scaling
- Consistent navbar-to-content spacing across all pages
- Bump cache version to v1.1.3

services/data-cleaning.php

@@ -12,7 +12,10 @@ $keywords = "data cleaning UK, data validation, duplicate removal, data standard
     <title><?php echo htmlspecialchars($page_title); ?></title>
     <meta name="description" content="<?php echo htmlspecialchars($page_description); ?>">
     <meta name="keywords" content="<?php echo htmlspecialchars($keywords); ?>">
-    <link rel="canonical" href="<?php echo htmlspecialchars($canonical_url); ?>">
+        <link rel="preconnect" href="https://fonts.googleapis.com">
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
+    <link href="https://fonts.googleapis.com/css2?family=Roboto+Slab:wght@100;200;300;400;500;600;700;800;900&family=Lato:wght@100;200;300;400;500;600;700;800;900&display=swap" rel="stylesheet">
+<link rel="canonical" href="<?php echo htmlspecialchars($canonical_url); ?>">
     
     <!-- Open Graph -->
     <meta property="og:title" content="<?php echo htmlspecialchars($page_title); ?>">