chore(dogfooding) improve desktop layout

[renefloor]

🎯 Goal

Describe why we are making this change
After making PR #845 I also wanted to make the app usable on wider displays. On multiple screens the layout breaks when you have a wide window.

🛠 Implementation details

Describe the implementation

On the home screen and the login screen I mainly made sure that the logo is not getting huge. I set the max width of that screen to 500px as the web implementation also doesn't get much wider than that. But we can discuss that value.

The lobby had the buttons weirdly aligned to the right, I added that to the max width that was already there.

The buttons on the call screen are very close to the bottom, so I added a bit of padding there.

🎨 UI Changes

Add relevant screenshots

Before	After

🧪 Testing

Explain how this change can be tested (or why it can't be tested)

To test the desktop changes you need to combine this branch with #845 to have it running on macos.
It should not effect smaller screens, but could be good to test on mobile devices as well.

☑️Contributor Checklist

General

• Assigned a person / code owner group (required)
• Thread with the PR link started in a respective Slack channel (#flutter-team) (required)
• PR is linked to the GitHub issue it resolves

☑️Reviewer Checklist

• Sample runs & works
• UI Changes correct (before & after images)
• Bugs validated (bugfixes)
• New feature tested and works
• All code we touched has new or updated Documentation

[xsahil03x]

Added few suggestions, overall looks good to me 🚀

[Brazol]

LGTM