FIX: Complete CodeMirror integration with native search, replace, and keyboard shortcuts

- Replace custom search/replace implementation with native CodeMirror extensions
- Add proper keyboard shortcut support: Ctrl+F, Ctrl+H, Ctrl+/, Ctrl+Space, etc.
- Fix browser shortcut conflicts by preventing defaults only when editor is focused
- Integrate autocompletion and comment toggle functionality
- Fix file name truncation in file manager grid to use text wrapping
- Add comprehensive keyboard shortcuts help panel for users
- Update i18n translations for editor buttons (Download, Replace, Replace All)
- Unify text and code file editing under single CodeMirror instance
- Add proper SSH HMAC algorithms for better compatibility

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/locales/en/translation.json

@@ -854,6 +854,9 @@
     "folderName": "Folder name",
     "find": "Find...",
     "replaceWith": "Replace with...",
+    "replace": "Replace",
+    "replaceAll": "Replace All",
+    "downloadInstead": "Download Instead",
     "startTyping": "Start typing...",
     "unknownSize": "Unknown size",
     "fileIsEmpty": "File is empty",

src/locales/zh/translation.json

@@ -877,6 +877,9 @@
     "folderName": "文件夹名",
     "find": "查找...",
     "replaceWith": "替换为...",
+    "replace": "替换",
+    "replaceAll": "全部替换",
+    "downloadInstead": "下载文件",
     "startTyping": "开始输入...",
     "fileSavedSuccessfully": "文件保存成功",
     "autoSaveFailed": "自动保存失败",