修复：移除 startWatching 中残留的 isModifiedExternally 引用（运行时 ReferenceError）

main.js

@@ -70,7 +70,6 @@ function startWatching(filePath) {
   try {
     fileWatcher = fs.watch(filePath, (eventType) => {
       if (eventType === 'change' && mainWindow && !mainWindow.isDestroyed()) {
-        isModifiedExternally = true;
         mainWindow.webContents.send('file:externallyModified', filePath);
       }
     });