feat: add instance lock and second instance handling

src/main/index.ts

@@ -7,6 +7,11 @@ import { registerZoomShortcut } from './shortcut'
 import { updateUserDataPath } from './utils/upgrade'
 import { createMainWindow } from './window'
 
+// Check for single instance lock
+if (!app.requestSingleInstanceLock()) {
+  app.quit()
+}
+
 // This method will be called when Electron has finished
 // initialization and is ready to create browser windows.
 // Some APIs can only be used after this event occurs.
@@ -42,6 +47,15 @@ app.whenReady().then(async () => {
   }
 })
 
+// Listen for second instance
+app.on('second-instance', () => {
+  const mainWindow = BrowserWindow.getAllWindows()[0]
+  if (mainWindow) {
+    mainWindow.isMinimized() && mainWindow.restore()
+    mainWindow.focus()
+  }
+})
+
 // Quit when all windows are closed, except on macOS. There, it's common
 // for applications and their menu bar to stay active until the user quits
 // explicitly with Cmd + Q.