fix: show window when app is rendered

[ShGKme]

☑️ Resolves

• ready-to-show only waits for an HTML document with resources to be loaded
• But then we need to request all async resources and mount a Vue app
• This is fast. But the loading is visible and feels like a web-page, not a desktop app
• Solution: show the window when the Vue app is mounted and the browser has rendered it
• This is slower. But doesn't feel like a web-page

But I cannot get rid of this white frame... Even when the window actually has a non-white background!

🖼️ Screenshots

🏚️ Before	🏡 After

By frame change:

🏚️ Before	🏡 After