Fix SSH encryption and add file download functionality

- Fix SSH authentication by ensuring all database operations use EncryptedDBOperations for automatic encryption/decryption
- Resolve SSH connection failures caused by encrypted password data being passed to authentication
- Add comprehensive file download functionality for SSH file manager (Issue #228)
- Update database migration to add require_password column for SSH sessions
- Enhance debugging and logging for SSH connection troubleshooting

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/locales/zh/translation.json

@@ -596,6 +596,7 @@
     "folder": "文件夹",
     "connectToSsh": "连接 SSH 以使用文件操作",
     "uploadFile": "上传文件",
+    "downloadFile": "下载文件",
     "newFile": "新建文件",
     "newFolder": "新建文件夹",
     "rename": "重命名",
@@ -608,7 +609,9 @@
     "clickToSelectFile": "点击选择文件",
     "chooseFile": "选择文件",
     "uploading": "上传中...",
+    "downloading": "下载中...",
     "uploadingFile": "正在上传 {{name}}...",
+    "downloadingFile": "正在下载 {{name}}...",
     "creatingFile": "正在创建 {{name}}...",
     "creatingFolder": "正在创建 {{name}}...",
     "deletingItem": "正在删除 {{type}} {{name}}...",
@@ -630,6 +633,10 @@
     "renaming": "重命名中...",
     "fileUploadedSuccessfully": "文件 \"{{name}}\" 上传成功",
     "failedToUploadFile": "上传文件失败",
+    "fileDownloadedSuccessfully": "文件 \"{{name}}\" 下载成功",
+    "failedToDownloadFile": "下载文件失败",
+    "noFileContent": "未收到文件内容",
+    "filePath": "文件路径",
     "fileCreatedSuccessfully": "文件 \"{{name}}\" 创建成功",
     "failedToCreateFile": "创建文件失败",
     "folderCreatedSuccessfully": "文件夹 \"{{name}}\" 创建成功",