Add global + page-scoped market listings with infinite scroll

- New all_markets blueprint at / with paginated grid and HTMX infinite scroll
- New page_markets blueprint at /<slug>/ for page-scoped market listing
- list_marketplaces service method (via shared submodule update)
- Updated slug preprocessor to handle both /<slug>/ and /<page_slug>/<market_slug>/
- Removed inline markets_listing() route (replaced by all_markets blueprint)

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

bp/__init__.py

@@ -1,2 +1,4 @@
 from .market.routes import register as register_market_bp
 from .product.routes import register as register_product
+from .all_markets.routes import register as register_all_markets
+from .page_markets.routes import register as register_page_markets