replaced account data singleton with a session model

lib/api/marianumcloud/webdav/webdav_api.dart

@@ -1,7 +1,7 @@
 import 'package:nextcloud/nextcloud.dart';
 
-import '../../../model/account_data.dart';
 import '../../../model/endpoint_data.dart';
+import '../../../session/session_manager.dart';
 import '../../api_response.dart';
 
 abstract class WebdavApi<T> {
@@ -20,8 +20,8 @@ abstract class WebdavApi<T> {
   static Future<WebDavClient> get webdav {
     // Keyed by user too: two accounts may share a password (no app password
     // minted), and the client would keep the previous login name.
-    final secret =
-        '${AccountData().getUsername()}:${AccountData().getNextcloudSecret()}';
+    final nextcloud = SessionManager().requireNextcloud();
+    final secret = '${nextcloud.username}:${nextcloud.secret}';
     if (_webdav == null || _webdavSecret != secret) {
       _webdavSecret = secret;
       _webdav = establishWebdavConnection();
@@ -33,13 +33,13 @@ abstract class WebdavApi<T> {
       NextcloudClient(
         Uri.parse('https://${EndpointData().nextcloud().full()}'),
         // App password preferred — with 2FA the real password is not accepted
-        // by Nextcloud at all (see AccountData.usesLoginFlow).
-        password: AccountData().getNextcloudSecret(),
-        loginName: AccountData().getUsername(),
+        // by Nextcloud at all (see NextcloudCredentials.usesLoginFlow).
+        password: SessionManager().requireNextcloud().secret,
+        loginName: SessionManager().requireNextcloud().username,
       ).webdav;
 
   /// Builds the WebDAV download URL without embedded credentials. Callers must
-  /// authenticate via the [AccountData.authHeaders] header instead.
+  /// authenticate via the [NextcloudCredentials.authHeaders] header instead.
   static String buildWebdavUrl() =>
-      'https://${EndpointData().nextcloud().full()}/remote.php/dav/files/${AccountData().getUsername()}/';
+      'https://${EndpointData().nextcloud().full()}/remote.php/dav/files/${SessionManager().requireNextcloud().username}/';
 }