feat(admin): separate platform CRUD from CMS, add entity selector macro

- Move platforms menu from CMS to Platform Admin section with create/edit
- Add platform create page, API endpoint, and service method
- Remove CMS-specific content from platform list and detail pages
- Create shared entity_selector + entity_selected_badge Jinja macros
- Create entity-selector.js generalizing store-selector.js for any entity
- Add Tom Select merchant filter to stores page with localStorage persistence
- Migrate store-products page to use shared macros (remove 53 lines of duped CSS)
- Fix broken icons: puzzle→puzzle-piece, building-storefront→store, language→translate, server→cube

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

app/modules/hosting/templates/hosting/admin/dashboard.html

@@ -66,7 +66,7 @@
         </a>
         <a href="/admin/hosting/clients"
            class="inline-flex items-center px-4 py-2 text-sm font-medium text-gray-700 bg-gray-200 rounded-lg hover:bg-gray-300 dark:text-gray-300 dark:bg-gray-700">
-            <span x-html="$icon('server', 'w-4 h-4 mr-2')"></span>
+            <span x-html="$icon('cube', 'w-4 h-4 mr-2')"></span>
             All Services
         </a>
     </div>