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/serial.types.ts

@@ -1,5 +1,7 @@
 export type SerialParity = 'none' | 'odd' | 'even'
 export type SerialFlowControl = 'none' | 'software' | 'hardware'
+/** What to send when the user presses Enter (UART has no PTY line discipline). */
+export type SerialLineEnding = 'lf' | 'cr' | 'crlf'
 
 export interface SerialConfig {
   path: string
@@ -8,6 +10,9 @@ export interface SerialConfig {
   stopBits: 1 | 2
   parity: SerialParity
   flowControl: SerialFlowControl
+  /** Optional local echo — only for serial (PTY backends must stay echo-off). */
+  localEcho?: boolean
+  lineEnding?: SerialLineEnding
 }
 
 export interface SerialPortSummary {