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>

core/status_checker.py

@@ -19,6 +19,7 @@ _SSH_TYPE = {"ssh"}
 _SQL_TYPES = {"mariadb", "mssql", "postgresql"}
 _REDIS_TYPE = {"redis"}
 _HTTP_TYPES = {"grafana", "prometheus", "winrm"}
+_S3_TYPE = {"s3"}
 _TCP_TYPES = {"telnet", "rdp", "vnc"}
 
 
@@ -60,6 +61,8 @@ class StatusChecker:
             return self._check_http(server, "/-/healthy")
         if server_type == "winrm":
             return self._check_http(server, "/wsman")
+        if server_type in _S3_TYPE:
+            return self._check_s3(server)
         if server_type in _TCP_TYPES:
             return self._check_tcp(server)
 
@@ -106,6 +109,17 @@ class StatusChecker:
         except Exception:
             return False
 
+    def _check_s3(self, server: dict) -> bool:
+        """Check S3 via list_buckets."""
+        try:
+            from core.s3_client import S3Client
+            client = S3Client(server)
+            result = client.connect()
+            client.disconnect()
+            return result
+        except Exception:
+            return False
+
     def _check_http(self, server: dict, path: str) -> bool:
         """Check HTTP(S) endpoint."""
         try: