feat(updater): stage3 resilient gui update flow

- added retry-based file copy, rollback restart, and version marker validation in updater GUI

- added build step to write dist/version.txt for post-update validation

- added unit tests for updater helpers

build.py

@@ -24,6 +24,18 @@ REMOVE_LIST = [
 ]
 
 
+def write_version_marker():
+    marker_path = os.path.join(DIST_DIR, "version.txt")
+    try:
+        os.makedirs(DIST_DIR, exist_ok=True)
+        with open(marker_path, "w", encoding="utf-8") as f:
+            f.write(str(VERSION).strip() + "\n")
+        print(f"[OK] Обновлен маркер версии: {marker_path}")
+    except Exception as e:
+        print(f"[ERROR] Не удалось записать version.txt: {e}")
+        sys.exit(1)
+
+
 def ensure_project_root():
     missing = [name for name in SAFE_CLEAN_ROOT_FILES if not os.path.exists(name)]
     if missing:
@@ -126,6 +138,7 @@ if __name__ == "__main__":
     run_build()
     run_updater_build()
     run_cleanup()
+    write_version_marker()
     create_archive()
 
     print("\n" + "=" * 30)