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

shared/types/host-metrics.types.ts

@@ -0,0 +1,26 @@
+export interface HostDiskMetric {
+  mount: string
+  percent: number
+  usedKb: number
+  totalKb: number
+}
+
+export interface HostMetrics {
+  /** /etc/os-release PRETTY_NAME, e.g. Ubuntu 24.04.4 LTS */
+  osPrettyName?: string
+  timezone?: string
+  timezoneOffset?: string
+  uptimeSec?: number
+  cpuPercent?: number
+  memUsedKb?: number
+  memTotalKb?: number
+  memPercent?: number
+  disks: HostDiskMetric[]
+}
+
+export interface HostMetricsResponse {
+  success: boolean
+  skipped?: boolean
+  metrics?: HostMetrics
+  error?: string
+}