v1.9.0: S3 server type — bucket/object browser, drag-and-drop upload, resilient transfers

New server type: S3 (MinIO, AWS, any S3-compatible storage)
- core/s3_client.py: boto3 client with auto-reconnect, 10 retries, exponential backoff, multipart upload/download, tcp_keepalive
- gui/tabs/s3_tab.py: object browser (Treeview), bucket selector, folder navigation, drag-and-drop upload from Explorer (windnd), progress bar with %, multi-file upload
- CLI: --s3-buckets, --s3-ls, --s3-upload, --s3-download, --s3-delete with retry
- ServerDialog: access_key, secret_key, bucket fields
- Registration: server_store, connection_factory, status_checker, icons, app, i18n (EN/RU/ZH)
- Fix: build.py cleanup_old_releases now sorts by semver (was lexicographic, broke v1.8.100+)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

version.py

@@ -1,6 +1,6 @@
 """Version info for ServerManager."""
 
-__version__ = "1.8.99"
+__version__ = "1.9.0"
 __app_name__ = "ServerManager"
 __author__ = "aibot777"
 __description__ = "Desktop GUI for managing remote servers"