feat(i18n): add multi-language support (ja/ko/vi/ru/zh-TW) with system auto-detection

- Extend AppLanguage to 7 locales: zh-CN, zh-TW, en, ja, ko, vi, ru
- Auto-detect system language via navigator.languages; fallback to English
- Add BCP47 locale mapping for date formatting and sorting
- Create 50 translation JSON files (5 languages × 10 namespaces, 1137 keys each)
- Update language selector with native language names
- Extend locale key parity test to cover all 7 languages (70 assertions)
- Add VNC/RDP desktop, serial terminal, AI agent, port forwarding, and SFTP features
- Add credential encryption, host metrics, session backup crypto, and zmodem bridge
- Update Rust backend: desktop services, host metrics, SSH/SFTP enhancements

src-tauri/src/services/ssh/sftp.rs

@@ -75,6 +75,36 @@ impl SshService {
         })
     }
 
+    pub fn sftp_upload_dir(
+        &self,
+        app: &AppHandle,
+        sftp_id: &str,
+        local_dir: &str,
+        remote_dir: &str,
+    ) -> Result<(), String> {
+        let sftp = self.sftp(sftp_id)?;
+        upload_dir(
+            &sftp,
+            &expand_home(local_dir),
+            remote_dir,
+            &mut |transferred, total| emit_progress(app, sftp_id, transferred, total),
+        )
+    }
+
+    pub fn sftp_download_dir(
+        &self,
+        app: &AppHandle,
+        sftp_id: &str,
+        remote_dir: &str,
+        local_dir: &str,
+    ) -> Result<(), String> {
+        let sftp = self.sftp(sftp_id)?;
+        let local_dir = expand_home(local_dir);
+        download_dir(&sftp, remote_dir, &local_dir, &mut |transferred, total| {
+            emit_progress(app, sftp_id, transferred, total)
+        })
+    }
+
     pub fn sftp_rename(
         &self,
         sftp_id: &str,
@@ -311,6 +341,140 @@ pub(super) fn download_file(
     fs::rename(&partial_path, local_path).map_err(|error| format!("提交下载文件失败: {error}"))
 }
 
+fn join_remote(parent: &str, name: &str) -> String {
+    if parent.is_empty() || parent == "/" {
+        format!("/{name}")
+    } else {
+        format!("{}/{name}", parent.trim_end_matches('/'))
+    }
+}
+
+fn is_dir_mode(mode: u32) -> bool {
+    mode & 0o170000 == 0o040000
+}
+
+fn ensure_remote_dir(sftp: &ssh2::Sftp, remote_dir: &str) -> Result<(), String> {
+    let normalized = if remote_dir.is_empty() {
+        "/".to_string()
+    } else {
+        remote_dir.trim_end_matches('/').to_string()
+    };
+    if normalized.is_empty() || normalized == "/" {
+        return Ok(());
+    }
+
+    let mut parts = Vec::new();
+    for part in normalized.trim_start_matches('/').split('/') {
+        if part.is_empty() || part == "." {
+            continue;
+        }
+        if part == ".." {
+            return Err("远程目录路径不能包含 ..".into());
+        }
+        parts.push(part);
+    }
+
+    let mut current = String::new();
+    for part in parts {
+        current = if current.is_empty() {
+            format!("/{part}")
+        } else {
+            format!("{current}/{part}")
+        };
+        match sftp.lstat(Path::new(&current)) {
+            Ok(stat) if is_dir_mode(stat.perm.unwrap_or(0)) => continue,
+            Ok(_) => return Err(format!("远程路径已存在且不是目录: {current}")),
+            Err(_) => {
+                sftp.mkdir(Path::new(&current), 0o755)
+                    .map_err(|error| format!("创建远程目录失败 ({current}): {error}"))?;
+            }
+        }
+    }
+    Ok(())
+}
+
+fn upload_dir(
+    sftp: &ssh2::Sftp,
+    local_dir: &Path,
+    remote_dir: &str,
+    progress: &mut dyn FnMut(u64, u64),
+) -> Result<(), String> {
+    let meta = fs::metadata(local_dir)
+        .map_err(|error| format!("读取本地目录失败 ({}): {error}", local_dir.display()))?;
+    if !meta.is_dir() {
+        return Err(format!("本地路径不是目录: {}", local_dir.display()));
+    }
+    ensure_remote_dir(sftp, remote_dir)?;
+
+    let mut entries = fs::read_dir(local_dir)
+        .map_err(|error| format!("遍历本地目录失败 ({}): {error}", local_dir.display()))?
+        .collect::<Result<Vec<_>, _>>()
+        .map_err(|error| format!("读取本地目录项失败: {error}"))?;
+    entries.sort_by_key(|entry| entry.file_name());
+
+    for entry in entries {
+        let file_type = entry
+            .file_type()
+            .map_err(|error| format!("读取本地文件类型失败: {error}"))?;
+        let name = entry.file_name().to_string_lossy().to_string();
+        if name == "." || name == ".." {
+            continue;
+        }
+        let local_child = entry.path();
+        let remote_child = join_remote(remote_dir, &name);
+        if file_type.is_dir() {
+            upload_dir(sftp, &local_child, &remote_child, progress)?;
+        } else if file_type.is_file() {
+            upload_file(sftp, &local_child, &remote_child, |transferred, total| {
+                progress(transferred, total)
+            })?;
+        }
+        // skip symlinks / special files for safety
+    }
+    Ok(())
+}
+
+fn download_dir(
+    sftp: &ssh2::Sftp,
+    remote_dir: &str,
+    local_dir: &Path,
+    progress: &mut dyn FnMut(u64, u64),
+) -> Result<(), String> {
+    let stat = sftp
+        .lstat(Path::new(remote_dir))
+        .map_err(|error| format!("读取远程目录失败 ({remote_dir}): {error}"))?;
+    if !is_dir_mode(stat.perm.unwrap_or(0)) {
+        return Err(format!("远程路径不是目录: {remote_dir}"));
+    }
+    fs::create_dir_all(local_dir)
+        .map_err(|error| format!("创建本地目录失败 ({}): {error}", local_dir.display()))?;
+
+    let mut entries = sftp
+        .readdir(Path::new(remote_dir))
+        .map_err(|error| format!("遍历远程目录失败 ({remote_dir}): {error}"))?;
+    entries.sort_by_key(|(path, _)| path.file_name().map(|name| name.to_os_string()));
+
+    for (path, entry_stat) in entries {
+        let name = match path.file_name() {
+            Some(value) => value.to_string_lossy().to_string(),
+            None => continue,
+        };
+        if name == "." || name == ".." {
+            continue;
+        }
+        let remote_child = join_remote(remote_dir, &name);
+        let local_child = local_dir.join(&name);
+        if is_dir_mode(entry_stat.perm.unwrap_or(0)) {
+            download_dir(sftp, &remote_child, &local_child, progress)?;
+        } else {
+            download_file(sftp, &remote_child, &local_child, |transferred, total| {
+                progress(transferred, total)
+            })?;
+        }
+    }
+    Ok(())
+}
+
 pub(super) fn copy_with_progress(
     reader: &mut impl Read,
     writer: &mut impl Write,