feat: add page admin market CRUD and update shared_lib

- Market create/delete routes in post admin blueprint
- markets.py service (create_market, soft_delete_market)
- _markets_panel.html admin template with HTMX create/delete
- Update shared_lib submodule (MarketPlace model, migration, URLs)

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

templates/_types/post/admin/_markets_panel.html

@@ -0,0 +1,44 @@
+<div id="markets-panel">
+  <h3 class="text-lg font-semibold mb-3">Markets</h3>
+
+  {% if markets %}
+  <ul class="space-y-2 mb-4">
+    {% for m in markets %}
+    <li class="flex items-center justify-between p-3 bg-stone-50 rounded">
+      <div>
+        <span class="font-medium">{{ m.name }}</span>
+        <span class="text-stone-400 text-sm ml-2">/{{ m.slug }}/</span>
+      </div>
+      <button
+        hx-delete="{{ url_for('blog.post.admin.delete_market', slug=post.slug, market_slug=m.slug) }}"
+        hx-target="#markets-panel"
+        hx-swap="outerHTML"
+        hx-confirm="Delete market '{{ m.name }}'?"
+        class="text-red-600 hover:text-red-800 text-sm"
+      >Delete</button>
+    </li>
+    {% endfor %}
+  </ul>
+  {% else %}
+  <p class="text-stone-500 mb-4 text-sm">No markets yet.</p>
+  {% endif %}
+
+  <form
+    hx-post="{{ url_for('blog.post.admin.create_market', slug=post.slug) }}"
+    hx-target="#markets-panel"
+    hx-swap="outerHTML"
+    class="flex gap-2"
+  >
+    <input
+      type="text"
+      name="name"
+      placeholder="Market name"
+      required
+      class="flex-1 border border-stone-300 rounded px-3 py-1.5 text-sm"
+    />
+    <button
+      type="submit"
+      class="bg-stone-800 text-white px-4 py-1.5 rounded text-sm hover:bg-stone-700"
+    >Create</button>
+  </form>
+</div>