fix: self-deactivation, UI overflow, Open With, archive nav, schedule modal

Settings - Delete Account -> Self Deactivate:
- backend: add POST /api/auth/self-deactivate (immediate, no email link)
  Guards against last-admin and hidden super-admin. Revokes FCM tokens,
  sends notification email, logs activity
- auth.js route: add /self-deactivate route
- auth_repository.dart: add requestSelfDeactivation()
- auth_provider.dart: add requestSelfDeactivation() (calls logout() after)
- settings_screen.dart: 2-step _handleDeactivateAccount: Step 1 confirm,
  Step 2 type DEACTIVATE. Danger zone card updated to deactivation theme

Report screen - compliance filter button label overflow:
- Wrap label Text in Flexible to ellipsize instead of clip

Settings - Edit Schedule Dates modal button overflow:
- Column layout on narrow screens so buttons are never squished

Document screen - Open With not working on Windows:
- Use openwith.exe (Windows 8+) with fallback to rundll32 OpenAs_RunDLL

Windows sidebar - Archive tab:
- Move Archives from ACCOUNT group to OVERVIEW group

frontend/lib/domain/repositories/auth_repository.dart

@@ -271,5 +271,22 @@ class AuthRepository {
       throw Exception(errorMessage);
     }
   }
+
+  /// Immediately deactivate own account (no email required — 2-step client confirmation)
+  Future<String> requestSelfDeactivation() async {
+    try {
+      final options = await _getAuthOptions();
+      final response = await _dio.post(
+        '/auth/self-deactivate',
+        options: options,
+      );
+      return response.data['message'] as String? ??
+          'Your account has been deactivated.';
+    } on DioException catch (e) {
+      final errorMessage =
+          e.response?.data['message'] ?? 'Failed to deactivate account.';
+      throw Exception(errorMessage);
+    }
+  }
 }