GDPR compliance: self-host all assets, add Impressum + Datenschutz

- Self-host Tailwind, Plotly, D3.js (no more CDN requests)
- Self-host Inter font (no more Google Fonts requests)
- Replace JetBrains Mono with system monospace font stack
- Zero external requests when visiting the site (GDPR-safe)
- Add /impressum page (§5 TMG, §18 MStV)
- Add /datenschutz page (DSGVO Art. 13/14)
- Hosting: Hetzner, no cookies, no tracking, no analytics
- Add Impressum/Datenschutz links to sidebar footer
- Configure Flask static_folder for local asset serving

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/webui/templates/authors.html

@@ -4,7 +4,7 @@
 {% block title %}Author Network — IETF Draft Analyzer{% endblock %}
 
 {% block extra_head %}
-<script src="https://d3js.org/d3.v7.min.js"></script>
+<script src="/static/js/d3.v7.min.js"></script>
 <style>
     #networkSvg {
         width: 100%;