feat(ui): add Impressum/Datenschutz footer links

remote.arcg.at has the same Medieninhaber (ARCG) as the homepage, so link the
legal pages there: Impressum -> amateurradioclubgraz.at/imprint/, Datenschutz ->
amateurradioclubgraz.at/datenschutz/ (the homepage DSE now covers the remote
station processing).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/index.html

@@ -551,6 +551,12 @@
       </nav>
     </main>
 
+    <footer class="site-footer">
+      <a href="https://amateurradioclubgraz.at/imprint/" target="_blank" rel="noopener noreferrer">Impressum</a>
+      <span class="site-footer-sep" aria-hidden="true">·</span>
+      <a href="https://amateurradioclubgraz.at/datenschutz/" target="_blank" rel="noopener noreferrer">Datenschutz</a>
+    </footer>
+
     <script src="/app.js" defer></script>
   </body>
 </html>