feat: Advanced file editor and file tree improvements (#444)

# Features
- File drag and drop upload: Support uploading files and folders via drag and drop
- Binary file handling: Detect binary files and display a friendly message instead of trying to edit them
- Folder download: Download folders as ZIP files (using JSZip library)
- Context menu integration: Full right-click context menu for file operations (rename, delete, copy path, download, new file/folder)

src/i18n/locales/ja/codeEditor.json

@@ -26,5 +26,9 @@
     "lines": "行数:",
     "characters": "文字数:",
     "shortcuts": "Ctrl+Sで保存 • Escで閉じる"
+  },
+  "binaryFile": {
+    "title": "バイナリファイル",
+    "message": "ファイル \"{{fileName}}\" はバイナリファイルのため、テキストエディタで表示できません。"
   }
 }