refactor: reorganize admin sidebar sections

- Move Background Tasks from Platform Health to Platform Monitoring
- Move Notifications from Settings to Platform Monitoring
- Rename Settings section to Platform Settings
- Update init-alpine.js page-to-section mappings

Platform Monitoring now contains: Import Jobs, Background Tasks,
Application Logs, and Notifications for centralized operational monitoring.

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

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

static/admin/js/init-alpine.js

@@ -80,15 +80,15 @@ function data() {
     // Platform Health
     testing: 'platformHealth',
     'code-quality': 'platformHealth',
-    'background-tasks': 'platformHealth',
     // Platform Monitoring
     imports: 'monitoring',
+    'background-tasks': 'monitoring',
     logs: 'monitoring',
-    // Settings
+    'notifications-settings': 'monitoring',
+    // Platform Settings
     settings: 'settingsSection',
     profile: 'settingsSection',
-    'api-keys': 'settingsSection',
-    'notifications-settings': 'settingsSection'
+    'api-keys': 'settingsSection'
   };
 
   return {