Make sidebar category/manufacturer sorting selectable

Kategorien and Hersteller/Quellen lists were hardcoded to sort by
count descending. Add a small dropdown (Name A-Z / Anzahl) above the
lists on both the Links and Prompts pages, backed by a new facet_sort
query param plumbed through facets()/prompt_facets(). Defaults to
alphabetical, which was the actual ask; count sort stays available
for anyone who preferred the old behavior. All sidebar facet links
carry the current facet_sort so it doesn't reset when filtering.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/templates/prompts.html

@@ -7,14 +7,23 @@
 <div class="layout">
   <aside class="sidebar">
     <div class="panel">
-      <a href="/prompts?sort={{ sort }}" class="facet {% if not active_category %}active{% endif %}">
+      <a href="/prompts?sort={{ sort }}&amp;facet_sort={{ facet_sort }}" class="facet {% if not active_category %}active{% endif %}">
         <span>{{ icons.grid(size=14) }} Alle Prompts</span>
       </a>
 
+      <div style="display:flex; justify-content:flex-end; margin-top:12px;">
+        <select onchange="const u=new URL(location); u.searchParams.set('facet_sort', this.value); location.href=u;"
+                title="Sortierung der Kategorie-Liste" style="font-size:.75rem; padding:3px 6px;">
+          {% for value, label in facet_sort_options.items() %}
+          <option value="{{ value }}" {% if facet_sort == value %}selected{% endif %}>{{ label }}</option>
+          {% endfor %}
+        </select>
+      </div>
+
       <div class="facet-group">
         <h3>Kategorien</h3>
         {% for name, count in facets.categories %}
-        <a href="/prompts?category={{ name | urlencode }}&amp;sort={{ sort }}"
+        <a href="/prompts?category={{ name | urlencode }}&amp;sort={{ sort }}&amp;facet_sort={{ facet_sort }}"
            class="facet {% if active_category == name %}active{% endif %}">
           <span>{{ name }}</span><span class="count">{{ count }}</span>
         </a>