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/i18n/locales/zh-TW/snippets.json

@@ -0,0 +1,32 @@
+{
+  "panel": {
+    "title": "命令片段"
+  },
+  "search": {
+    "placeholder": "搜尋片段..."
+  },
+  "form": {
+    "name": "名稱",
+    "command": "命令",
+    "tags": "標籤",
+    "tagsHint": "(以逗號分隔)",
+    "namePlaceholder": "例如：重啟 Nginx",
+    "commandPlaceholder": "sudo systemctl restart nginx\n# 支援 {{host}} {{username}} {{date}}",
+    "variables": "變數："
+  },
+  "dialog": {
+    "createTitle": "新增片段",
+    "editTitle": "編輯片段"
+  },
+  "empty": {
+    "noMatch": "沒有符合的片段",
+    "noMatchDesc": "嘗試其他關鍵字搜尋",
+    "noSnippets": "暫無片段",
+    "noSnippetsDesc": "儲存常用命令，快速插入到終端機"
+  },
+  "action": {
+    "create": "新增片段",
+    "insert": "插入到終端機",
+    "noTerminal": "無活躍終端機"
+  }
+}