fix: use confirm_modal macro instead of browser confirm for platform removal

Replaced the native browser confirm() dialog with the styled confirm_modal
macro for a consistent UI experience when removing platform assignments
from admin users.

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

app/templates/admin/admin-user-edit.html

@@ -2,6 +2,7 @@
 {% extends "admin/base.html" %}
 {% from 'shared/macros/alerts.html' import loading_state %}
 {% from 'shared/macros/headers.html' import edit_page_header %}
+{% from 'shared/macros/modals.html' import confirm_modal %}
 
 {% block title %}Edit Admin User{% endblock %}
 
@@ -252,6 +253,18 @@
         </div>
     </div>
 </div>
+
+<!-- Remove Platform Confirmation Modal -->
+{{ confirm_modal(
+    'removePlatformModal',
+    'Remove Platform',
+    'Are you sure you want to remove this platform from this admin?',
+    'confirmRemovePlatform()',
+    'showRemovePlatformModal',
+    'Remove',
+    'Cancel',
+    'warning'
+) }}
 {% endblock %}
 
 {% block extra_scripts %}

static/admin/js/admin-user-edit.js

@@ -23,6 +23,10 @@ function adminUserEditPage() {
         availablePlatforms: [],
         selectedPlatformId: null,
 
+        // Confirmation modal state
+        showRemovePlatformModal: false,
+        platformToRemove: null,
+
         // Initialize
         async init() {
             adminUserEditLog.info('=== ADMIN USER EDIT PAGE INITIALIZING ===');
@@ -237,22 +241,23 @@ function adminUserEditPage() {
             }
         },
 
-        // Remove platform from admin
-        async removePlatform(platformId) {
-            const platform = this.adminUser.platforms.find(p => p.id === platformId);
-            const platformName = platform ? platform.name : platformId;
-
+        // Show confirmation modal for platform removal
+        removePlatform(platformId) {
             // Validate: platform admin must have at least one platform
             if (this.adminUser.platforms.length <= 1) {
                 Utils.showToast('Platform admin must be assigned to at least one platform', 'error');
                 return;
             }
 
-            if (!confirm(`Are you sure you want to remove "${platformName}" from this admin?`)) {
-                adminUserEditLog.info('Platform removal cancelled by user');
-                return;
-            }
+            this.platformToRemove = this.adminUser.platforms.find(p => p.id === platformId);
+            this.showRemovePlatformModal = true;
+        },
 
+        // Confirm and execute platform removal
+        async confirmRemovePlatform() {
+            if (!this.platformToRemove) return;
+
+            const platformId = this.platformToRemove.id;
             adminUserEditLog.info('Removing platform:', platformId);
             this.saving = true;
 
@@ -275,6 +280,7 @@ function adminUserEditPage() {
                 Utils.showToast(error.message || 'Failed to remove platform', 'error');
             } finally {
                 this.saving = false;
+                this.platformToRemove = null;
             }
         },