fix(ui): Senden als runder Icon-Button (Fußzeile überlaufsicher)

- Senden ➤ als runder Icon-Button (gleich groß wie Mikrofon) statt Text -> passt
  auch im Querformat/schmalen Geräten, kein Abschneiden mehr.
- Eingabefeld min-w-0, Buttons shrink-0 -> Reihe kann nicht überlaufen.

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

app/web/index.html

@@ -290,16 +290,20 @@
 
   <footer class="shrink-0 border-t border-slate-200 dark:border-slate-700 bg-white dark:bg-slate-800 px-3 pt-3 pb-[calc(env(safe-area-inset-bottom)+0.6rem)]">
     <form id="prompt-form" class="flex items-center gap-2 w-full max-w-3xl mx-auto">
-      <button type="button" id="mic" title="Mikrofon"
+      <button type="button" id="mic" title="Mikrofon" aria-label="Mikrofon"
         class="shrink-0 h-11 w-11 grid place-items-center rounded-full bg-emerald-600 text-white text-lg">🎤</button>
       <input id="prompt" type="text" autocomplete="off" placeholder="Nachricht …"
-        class="flex-1 rounded-xl border border-slate-300 dark:border-slate-600 bg-transparent px-4 py-2.5 focus:outline-none focus:ring-2 focus:ring-blue-500" />
+        class="flex-1 min-w-0 rounded-xl border border-slate-300 dark:border-slate-600 bg-transparent px-4 py-2.5 focus:outline-none focus:ring-2 focus:ring-blue-500" />
-      <button type="submit" id="send"
+      <button type="submit" id="send" title="Senden" aria-label="Senden"
-        class="shrink-0 rounded-xl bg-blue-600 hover:bg-blue-700 text-white px-4 py-2.5 font-medium transition-colors">Senden</button>
+        class="shrink-0 h-11 w-11 grid place-items-center rounded-full bg-blue-600 hover:bg-blue-700 text-white transition-colors">
+        <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" class="w-5 h-5">
+          <path stroke-linecap="round" stroke-linejoin="round" d="M6 12 3.27 4.36a.6.6 0 0 1 .82-.74l16.2 7.83a.6.6 0 0 1 0 1.08l-16.2 7.83a.6.6 0 0 1-.82-.74L6 12Zm0 0h7" />
+        </svg>
+      </button>
     </form>
     <div id="status" class="w-full max-w-3xl mx-auto mt-1 min-h-[1rem] text-xs text-slate-500 dark:text-slate-400"></div>
   </footer>
 
-  <script src="/app.js?v=35"></script>
+  <script src="/app.js?v=36"></script>
 </body>
 </html>