refactor: rename Product Catalog to Vendor Operations

- Rename sidebar section from "Product Catalog" to "Vendor Operations"
- Change section key from 'productCatalog' to 'vendorOps'
- Add placeholder comments for future items (Inventory, Orders, Shipping)
- Update pageSectionMap in init-alpine.js

This prepares the sidebar for expanded vendor management capabilities
including inventory, orders, and shipping management.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/templates/admin/partials/sidebar.html

@@ -75,11 +75,16 @@
         {{ menu_item('customers', '/admin/customers', 'user-group', 'Customers') }}
     {% endcall %}
 
-    <!-- Product Catalog Section -->
-    {{ section_header('Product Catalog', 'productCatalog') }}
-    {% call section_content('productCatalog') %}
+    <!-- Vendor Operations Section -->
+    {{ section_header('Vendor Operations', 'vendorOps') }}
+    {% call section_content('vendorOps') %}
         {{ menu_item('marketplace-products', '/admin/marketplace-products', 'database', 'Marketplace Products') }}
         {{ menu_item('vendor-products', '/admin/vendor-products', 'cube', 'Vendor Products') }}
+        {# Future items - uncomment when implemented:
+        {{ menu_item('inventory', '/admin/inventory', 'archive', 'Inventory') }}
+        {{ menu_item('orders', '/admin/orders', 'clipboard-list', 'Orders') }}
+        {{ menu_item('shipping', '/admin/shipping', 'truck', 'Shipping') }}
+        #}
     {% endcall %}
 
     <!-- Marketplace Section -->