v1.8.4: fix FilesTab showing stale remote files on server switch

- Clear remote panel immediately when switching servers
- Add race condition guards in async SFTP connect/refresh
- Validate alias at each async callback to prevent stale UI updates
- Add switching_servers/disconnected/sftp_server_not_found i18n keys
- Properly handle connection results arriving after server switch

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

core/i18n.py

@@ -277,6 +277,9 @@ _EN = {
     "items_count": "{count} items",
     "sudo_mode": "Sudo",
     "try_sudo_hint": "Try enabling Sudo mode",
+    "switching_servers": "Switching servers...",
+    "disconnected": "Disconnected",
+    "sftp_server_not_found": "[!] Server not found",
     "uploading_dir": "Uploading folder: {name}",
     "downloading_dir": "Downloading folder: {name}",
     "transfer_file_progress": "File {cur}/{total}: {name}",
@@ -539,6 +542,9 @@ _RU = {
     "items_count": "{count} элементов",
     "sudo_mode": "Sudo",
     "try_sudo_hint": "Попробуйте включить Sudo",
+    "switching_servers": "Переключение серверов...",
+    "disconnected": "Отключено",
+    "sftp_server_not_found": "[!] Сервер не найден",
     "uploading_dir": "Загрузка папки: {name}",
     "downloading_dir": "Скачивание папки: {name}",
     "transfer_file_progress": "Файл {cur}/{total}: {name}",
@@ -801,6 +807,9 @@ _ZH = {
     "items_count": "{count} 个项目",
     "sudo_mode": "Sudo",
     "try_sudo_hint": "尝试启用Sudo模式",
+    "switching_servers": "切换服务器...",
+    "disconnected": "已断开",
+    "sftp_server_not_found": "[!] 未找到服务器",
     "uploading_dir": "上传文件夹: {name}",
     "downloading_dir": "下载文件夹: {name}",
     "transfer_file_progress": "文件 {cur}/{total}: {name}",