fix: update market template to use container refs, add config

- Template uses m.page.slug instead of m.post.slug
- Add app-config.yaml

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

templates/_types/market/markets_listing.html

@@ -7,7 +7,7 @@
   {% if markets %}
   <div class="grid gap-4">
     {% for m in markets %}
-    <a href="/{{ m.post.slug }}/{{ m.slug }}/"
+    <a href="/{{ m.page.slug }}/{{ m.slug }}/"
        class="block p-6 bg-white border border-stone-200 rounded-lg hover:border-stone-400 transition-colors">
       <h2 class="text-lg font-semibold">{{ m.name }}</h2>
       {% if m.description %}