Complete Settings page and fix TypeScript issues

- Create comprehensive SettingsPage with General, Storage, and Security tabs
- Add formatBytes method to settings service
- Update AdminSidebar to show real storage usage from backend
- Fix TypeScript errors with react-query v5 (isPending instead of isLoading)
- Remove unused imports and fix type imports
- Add Settings route to App.tsx
- Implement real-time storage monitoring in sidebar

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

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

frontend/src/services/settings.service.ts

@@ -93,5 +93,14 @@ export const settingsService = {
   // Format theme settings from raw data
   formatThemeSettings(rawSettings: Record<string, any>): ThemeSettings {
     return rawSettings.theme_config || {};
+  },
+
+  // Format bytes to human readable
+  formatBytes(bytes: number): string {
+    if (bytes === 0) return '0 Bytes';
+    const k = 1024;
+    const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
+    const i = Math.floor(Math.log(bytes) / Math.log(k));
+    return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
   }
 };