consolidated downloads dir, nextcloud origin, upload route and chat timestamps; added webdav path tests

lib/api/marianumcloud/webdav/webdav_api.dart

@@ -31,7 +31,7 @@ abstract class WebdavApi<T> {
 
   static Future<WebDavClient> establishWebdavConnection() async =>
       NextcloudClient(
-        Uri.parse('https://${EndpointData().nextcloud().full()}'),
+        Uri.parse(EndpointData().nextcloud().origin()),
         // App password preferred — with 2FA the real password is not accepted
         // by Nextcloud at all (see NextcloudCredentials.usesLoginFlow).
         password: SessionManager().requireNextcloud().secret,
@@ -41,5 +41,5 @@ abstract class WebdavApi<T> {
   /// Builds the WebDAV download URL without embedded credentials. Callers must
   /// authenticate via the [NextcloudCredentials.authHeaders] header instead.
   static String buildWebdavUrl() =>
-      'https://${EndpointData().nextcloud().full()}/remote.php/dav/files/${SessionManager().requireNextcloud().username}/';
+      '${EndpointData().nextcloud().origin()}/remote.php/dav/files/${SessionManager().requireNextcloud().username}/';
 }