Add imprint page with privacy/attribution info and footer link

Adds /imprint/ with operator contact, self-hosted Umami analytics
disclosure, content attribution, and disclaimer sections. Links
Imprint in the footer bottom bar next to the pivoine.art credit.

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

layouts/partials/footer.html

@@ -50,7 +50,10 @@
     <!-- Bottom bar -->
     <div class="flex justify-between items-center mt-[54px] pt-6 border-t border-warm/10">
       <span class="font-mono text-[11px] text-ink-faint tracking-[0.04em]">© 2026 Bar Pivoine</span>
-      <span class="font-mono text-[11px] text-ink-faint tracking-[0.04em]">Powered by <a href="https://pivoine.art" class="hover:text-ink transition-colors duration-[180ms]">pivoine.art</a></span>
+      <div class="flex items-center gap-5">
+        <a href="/imprint/" class="font-mono text-[11px] text-ink-faint tracking-[0.04em] hover:text-ink transition-colors duration-[180ms]">Imprint</a>
+        <span class="font-mono text-[11px] text-ink-faint tracking-[0.04em]">Powered by <a href="https://pivoine.art" class="hover:text-ink transition-colors duration-[180ms]">pivoine.art</a></span>
+      </div>
     </div>
 
   </div>