feat: add modular impressum.js, replace martinsiebels.de with msbls.de

- shared/impressum.js: configurable via data-owner and data-style attrs
- Default: minimal msbls.de attribution for satire sites
- Build now copies shared/ to build output
- Caddyfile serves /shared/* globally across all domains
- Removed martinsiebels.de references from 7 KI-satire sites

sites/kilibri.de/index.html

@@ -267,8 +267,9 @@
   <footer>
     <div class="container">
       <p>🐦 <span class="ki">KI</span>libri — Klein, schnell, bunt. Die <span class="ki">KI</span> für dein Nest.</p>
-      <p style="margin-top: 8px;">Ein Projekt von <a href="https://martinsiebels.de" style="color: var(--teal); text-decoration: none;">martinsiebels.de</a></p>
+      
     </div>
   </footer>
+  <script src="/shared/impressum.js"></script>
 </body>
 </html>