chore: Refactor Dockerfile and update HTML favicon links

- Simplify Dockerfile by removing redundant BASE_URL handling logic and complex RUN commands
- Change SIMPLE_MODE default from true to false for production builds
- Fix indentation inconsistencies in Dockerfile conditional statements
- Move favicon link tags from body to head section in all HTML files for proper semantic structure
- Replace inline favicon links with img tag in navigation logo across all pages
- Update README.md documentation to clarify BASE_URL trailing slash requirements
- Remove commented-out legacy Dockerfile code for cleaner maintenance
- Consolidate favicon declarations in document head for better performance and SEO

src/pages/edit-attachments.html

@@ -10,6 +10,7 @@
     <link rel="icon" type="image/svg+xml" href="/images/favicon.svg" />
     <link rel="icon" type="image/png" href="/images/favicon.png" />
     <link rel="apple-touch-icon" href="/images/favicon.png" />
+    <link rel="icon" href="/favicon.ico" sizes="any" />
     <link rel="alternate" hreflang="en" href="/en/edit-attachments.html" />
     <link rel="alternate" hreflang="de" href="/de/edit-attachments.html" />
     <link rel="alternate" hreflang="x-default" href="/en/edit-attachments.html" />