feat(legal): add impressum and datenschutz pages

Fix #29: Create impressum.html with full §5 TMG details and
datenschutz.html with DSGVO-compliant privacy policy.
Fix footer links in main page. Both pages use landingpage design,
have meta robots noindex, and are responsive.

haus-schleusingen.html

@@ -592,8 +592,8 @@
     <footer>
       <div class="footer-logo">Bahnhofstraße 10 · Schleusingen</div>
       <div class="footer-links">
-        <a href="/impressum" target="_blank">Impressum</a>
-        <a href="/datenschutz" target="_blank">Datenschutz</a>
+        <a href="impressum.html">Impressum</a>
+        <a href="datenschutz.html">Datenschutz</a>
       </div>
     </footer>