make auth flow possible to complete in dev

[szymonkaliski]

Why

Our auth flow relies on deeplinks (mainly, opening replit://authComplete?authToken=...). Deeplinks are not supported in dev so we currently can't log in using an unpackaged app. Honestly I have no idea if/how we used this in the past.

This PR adds a "Complete Auth From Clipboard" menu item (only in dev -- unpackaged app) which allows us to complete the auth flow in dev, by copying the callback URL from the browser, and clicking that menu item.

What changed

As described above.

Test plan

• run the web app on localhost
• pnpm start:local in desktop
• click login - see the flow complete but new empty electron opens (this is expected) - close that window
• go to browser and copy the URL (should look like: http://localhost:3000/desktopApp/authSuccess?authToken=...)
• click the menu item - get logged in!