fix: rsync progress callback overwritten by SnapshotManager

SnapshotManager::create_snapshot() set rsync_.on_progress = on_progress
where on_progress was nullptr, destroying the MainWindow callback.

Removed the line — MainWindow already sets rsync_.on_progress in ctor.

src/snapshot_manager.cpp

@@ -37,7 +37,8 @@ std::string SnapshotManager::create_snapshot(const std::string& description) {
 		link_dest = snapshots[0].path;
 	}
 
-	rsync_.on_progress = on_progress;
+	/* Do NOT overwrite rsync_.on_progress — MainWindow already set it */
+
 	bool ok = rsync_.create_snapshot(ts, config_.settings().source_path, snapshots_dir, link_dest);
 
 	if (ok) {