fix: QA audit bugs BUG-051/052/056/057/059/062/063/064/065/066/068

- BUG-056: Fix sitemap namespace sitemapns.org -> sitemaps.org
- BUG-062: Extend <main> to wrap all page content (hero+features+pricing+EU section)
- BUG-064: Add sr-only <label> elements to all modal form inputs (signup, recovery, change-email)
- BUG-051/052: Remove duplicate X-Content-Type-Options headers from nginx (let helmet handle)
- BUG-057: Fix JSON-LD and pricing card: Pro plan is 2,500 PDFs/month not 5,000
- BUG-059: Add meta description, canonical URL, og: tags to /docs page
- BUG-063: Change eu-hosting h3 to h2 (correct heading hierarchy)
- BUG-065/066: Add aria-modal=true, role=dialog to modals; aria-label=Close to close buttons
- BUG-068: Add hash-based modal open for #change-email on page load
- Add .sr-only CSS utility class to base and index styles

templates/pages/docs.html

@@ -4,6 +4,16 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>DocFast API Documentation</title>
+  <meta name="description" content="DocFast API documentation. Learn how to convert HTML and Markdown to PDF with a simple REST API call. Endpoints, authentication, templates, and examples.">
+  <link rel="canonical" href="https://docfast.dev/docs">
+  <meta property="og:title" content="DocFast API Documentation">
+  <meta property="og:description" content="Convert HTML and Markdown to PDF with a simple REST API call. Full API reference with examples.">
+  <meta property="og:type" content="website">
+  <meta property="og:url" content="https://docfast.dev/docs">
+  <meta property="og:image" content="https://docfast.dev/og-image.png">
+  <meta name="twitter:card" content="summary_large_image">
+  <meta name="twitter:title" content="DocFast API Documentation">
+  <meta name="twitter:description" content="Convert HTML and Markdown to PDF with a simple REST API call.">
   <link rel="icon" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100 100'><text y='.9em' font-size='90'>⚡</text></svg>">
   <link rel="stylesheet" href="/swagger-ui/swagger-ui.css">
   <style>