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

src/partials/footer.html

@@ -15,7 +15,7 @@
         <p id="footer-copyright" class="text-gray-400 text-sm" {{#unless footerText}}data-i18n="footer.copyright"{{/unless}}>
           {{#if footerText}}{{footerText}}{{else}}&copy; 2026 BentoPDF. All rights reserved.{{/if}}
         </p>
-        <p class="text-gray-500 text-xs mt-2">
+        <p class="text-gray-400 text-xs mt-2">
           <span data-i18n="footer.version">Version</span>
           <span id="app-version">{{appVersion}}</span>
         </p>