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/domain/ssh.rs

@@ -101,6 +101,34 @@ impl IdResponse {
     }
 }
 
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ShellOutputResponse {
+    pub success: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub data: Option<Vec<u8>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub error: Option<String>,
+}
+
+impl ShellOutputResponse {
+    pub fn ok(data: Vec<u8>) -> Self {
+        Self {
+            success: true,
+            data: Some(data),
+            error: None,
+        }
+    }
+
+    pub fn error(error: impl Into<String>) -> Self {
+        Self {
+            success: false,
+            data: None,
+            error: Some(error.into()),
+        }
+    }
+}
+
 #[derive(Debug, Serialize)]
 #[serde(rename_all = "camelCase")]
 pub struct ExecResponse {
@@ -212,3 +240,76 @@ pub struct SftpProgressEvent {
     pub total: u64,
     pub percentage: u8,
 }
+
+#[derive(Debug, Serialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct HostDiskMetric {
+    pub mount: String,
+    pub percent: u8,
+    pub used_kb: u64,
+    pub total_kb: u64,
+}
+
+#[derive(Debug, Serialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct HostMetrics {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub os_pretty_name: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub timezone: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub timezone_offset: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub uptime_sec: Option<u64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cpu_percent: Option<f32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub mem_used_kb: Option<u64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub mem_total_kb: Option<u64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub mem_percent: Option<u8>,
+    pub disks: Vec<HostDiskMetric>,
+}
+
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct HostMetricsResponse {
+    pub success: bool,
+    /// True when another ssh_exec (e.g. Agent) holds the connection — caller should keep stale UI.
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub skipped: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub metrics: Option<HostMetrics>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub error: Option<String>,
+}
+
+impl HostMetricsResponse {
+    pub fn ok(metrics: HostMetrics) -> Self {
+        Self {
+            success: true,
+            skipped: false,
+            metrics: Some(metrics),
+            error: None,
+        }
+    }
+
+    pub fn skipped() -> Self {
+        Self {
+            success: true,
+            skipped: true,
+            metrics: None,
+            error: None,
+        }
+    }
+
+    pub fn error(error: impl Into<String>) -> Self {
+        Self {
+            success: false,
+            skipped: false,
+            metrics: None,
+            error: Some(error.into()),
+        }
+    }
+}