fix: apply QA fixes to correct build source (public/src/)

- BUG-055: Remove duplicate preconnect tags from homepage
- BUG-058: Add twitter:image meta tag to homepage
- BUG-060: Add og:title/description/url to sub-pages (impressum/privacy/terms/status)
- BUG-061: Already done in sitemap.xml
- BUG-067: Add skip-to-content link via nav partial + styles_base
- BUG-069: Footer already added to docs.html
- BUG-053: Minify app.js and status.js, update HTML refs

public/partials/_nav.html

@@ -1,3 +1,4 @@
+<a href="#main" class="skip-link">Skip to content</a>
 <nav aria-label="Main navigation">
   <div class="container">
     <a href="/" class="logo">⚡ Doc<span>Fast</span></a>