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/desktop.types.ts

@@ -0,0 +1,95 @@
+/** Shared remote-desktop (RDP / VNC) contracts for the renderer. */
+
+export type DesktopProtocol = 'rdp' | 'vnc'
+
+export type DesktopSecurity = 'nla' | 'tls' | 'rdp' | 'auto'
+
+export interface RdpConfig {
+  host: string
+  port?: number
+  username: string
+  password: string
+  domain?: string
+  /** Default NLA (CredSSP). */
+  security?: DesktopSecurity
+  width?: number
+  height?: number
+}
+
+export interface VncConfig {
+  host: string
+  port?: number
+  /** Optional VNC password (DES challenge). */
+  password?: string
+  width?: number
+  height?: number
+}
+
+export type DesktopSessionConfig =
+  | { protocol: 'rdp'; config: RdpConfig }
+  | { protocol: 'vnc'; config: VncConfig }
+
+export interface DesktopOpenResponse {
+  sessionId: string
+}
+
+export interface DesktopStatusEvent {
+  sessionId: string
+  status: 'connecting' | 'connected' | 'disconnected' | 'error'
+  message?: string
+  width?: number
+  height?: number
+}
+
+/** Dirty-rectangle frame. Prefer JPEG (`encoding: 'jpeg'`); `rgba` is raw w*h*4 fallback. */
+export interface DesktopFrameEvent {
+  sessionId: string
+  x: number
+  y: number
+  width: number
+  height: number
+  /** Full framebuffer width (for canvas sizing). */
+  fbWidth: number
+  /** Full framebuffer height. */
+  fbHeight: number
+  encoding: 'jpeg' | 'rgba'
+  dataBase64: string
+}
+
+export type DesktopPointerButton = 'left' | 'middle' | 'right' | 'wheel_up' | 'wheel_down'
+
+export interface DesktopPointerEvent {
+  x: number
+  y: number
+  button?: DesktopPointerButton
+  pressed?: boolean
+  /** true = pointer move (may include held button for drag). */
+  moving?: boolean
+}
+
+export interface DesktopKeyEvent {
+  key: string
+  code: string
+  pressed: boolean
+  altKey?: boolean
+  ctrlKey?: boolean
+  metaKey?: boolean
+  shiftKey?: boolean
+}
+
+export interface RdpClipboardEvent {
+  sessionId: string
+  text: string
+}
+
+export interface VncClipboardEvent {
+  sessionId: string
+  text: string
+}
+
+export interface RdpFileDownloadEvent {
+  sessionId: string
+  name: string
+  /** Absolute path in the host Downloads folder. */
+  path: string
+}