feat: implement admin-users management with super admin restriction

- Add /admin/admin-users routes for managing admin users (super admin only)
- Remove vendor role from user creation form (vendors created via company hierarchy)
- Add admin-users.html and admin-user-detail.html templates
- Add admin-users.js and admin-user-detail.js for frontend logic
- Move database operations to admin_platform_service (list, get, create, delete, toggle status)
- Update sidebar to show Admin Users section only for super admins
- Add isSuperAdmin computed property to init-alpine.js
- Fix /api/v1 prefix issues in JS files (apiClient already adds prefix)
- Update architecture rule JS-012 to catch more variable patterns (url, endpoint, path)
- Replace inline SVGs with $icon() helper in select-platform.html

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

static/admin/js/login.js

@@ -187,7 +187,7 @@ function adminLogin() {
                 // Check if platform selection is required
                 try {
                     loginLog.info('Checking accessible platforms...');
-                    const platformsResponse = await apiClient.get('/api/v1/admin/auth/accessible-platforms');
+                    const platformsResponse = await apiClient.get('/admin/auth/accessible-platforms');
                     loginLog.debug('Accessible platforms response:', platformsResponse);
 
                     if (platformsResponse.requires_platform_selection) {