feat: restructure market app with per-market URL scoping

- URL structure changes from /<route> to /<market_slug>/<route>
- Root / shows markets listing page
- app.py: url_value_preprocessor, url_defaults, hydrate_market (events app pattern)
- Browse queries (db_nav, db_products_nocounts, db_products_counts) accept market_id
- _productInfo reads g.market.id to scope all queries
- save_nav accepts market_id, sets on new NavTop rows
- API save_nav passes g.market.id
- Scraper default URLs point to /suma-market/ on port 8001

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

templates/_types/market/markets_listing.html

@@ -0,0 +1,23 @@
+{% extends '_types/root/_index.html' %}
+
+{% block content %}
+<div class="max-w-3xl mx-auto py-8 px-4">
+  <h1 class="text-2xl font-bold mb-6">Markets</h1>
+
+  {% if markets %}
+  <div class="grid gap-4">
+    {% for m in markets %}
+    <a href="/{{ 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 %}
+      <p class="text-stone-600 mt-1">{{ m.description }}</p>
+      {% endif %}
+    </a>
+    {% endfor %}
+  </div>
+  {% else %}
+  <p class="text-stone-500">No markets available.</p>
+  {% endif %}
+</div>
+{% endblock %}