simplified code across the app and consolidated duplicated helpers

lib/api/marianumcloud/app_password/delete_app_password.dart

@@ -18,13 +18,7 @@ class DeleteAppPassword {
       NextcloudOcs.uri('core/apppassword'),
       // An explicit header may belong to an inactive account, so the active
       // session's headers must not be required then.
-      headers: authorizationHeader == null
-          ? NextcloudOcs.headers()
-          : {
-              'Accept': 'application/json',
-              'OCS-APIRequest': 'true',
-              'Authorization': authorizationHeader,
-            },
+      headers: NextcloudOcs.headers(authorization: authorizationHeader),
     );
   }
 }

lib/api/marianumcloud/app_password/get_app_password.dart

@@ -28,23 +28,17 @@ class GetAppPassword {
       label,
       () => _client.get(
         NextcloudOcs.uri('core/getapppassword'),
-        headers: {
-          ...NextcloudOcs.headers(),
-          // Deliberately NOT the shared Authorization value: that one prefers
-          // the app password, but an app password cannot mint another one —
-          // this endpoint requires the real password.
-          'Authorization': SessionManager()
+        // Deliberately NOT the shared Authorization value: that one prefers
+        // the app password, but an app password cannot mint another one —
+        // this endpoint requires the real password.
+        headers: NextcloudOcs.headers(
+          authorization: SessionManager()
               .requireNextcloud()
               .realPasswordBasicAuthHeader,
-        },
+        ),
       ),
     ))!;
-    if (response.statusCode < 200 || response.statusCode >= 300) {
-      throwForStatus(
-        response.statusCode,
-        httpErrorDetail(label, response.body, response.statusCode),
-      );
-    }
+    ensureSuccess(label, response);
     final json = jsonDecode(utf8.decode(response.bodyBytes));
     final data = (json as Map)['ocs']?['data'];
     final appPassword = data is Map ? data['apppassword'] as String? : null;