feat(seo): canonicalize URLs, clean structured data, add audit gate

- Canonicals/hreflang/og point to www.bentopdf.com everywhere
- Drop fake aggregateRating; add Organization + breadcrumb JSON-LD
- Sitemap: filter 404/wasm-settings, mtime-based lastmod
- Rename locale ua → uk (correct ISO 639-1)
- Self-hoster: SITE_URL build arg, ROBOTS_NOINDEX runtime env
- Simple Mode indexable by default
- nginx: collapse .html and /index.html via 301
- SEO audit script + PR gate; runtime config noise fixed
- a11y contrast fix; language switcher gets search + scroll
- robots.txt: drop Crawl-delay

pdf-editor.html

@@ -18,7 +18,7 @@
     <meta name="robots" content="index, follow, max-image-preview:large" />
 
     <!-- Canonical URL -->
-    <link rel="canonical" href="https://www.bentopdf.com/pdf-editor.html" />
+    <link rel="canonical" href="https://www.bentopdf.com/pdf-editor" />
 
     <!-- Open Graph -->
     <meta property="og:type" content="website" />