improve error messages in the client

[ghost]

It would be really helpful when the macOS/iOS app also shows the URL that was contacted that generates an error so we can figure out what exactly causes the problem. Now it just fills the screen with (part of) the response, but no context.

[ghost]

Other approach: provide a button the user can click to get the full request/response bodies so we know exactly what is going on. Or jump to the exact position in the log file where error details are shown.

[ghost]

As an example, this is very much not helpful:

[ghost]

This is actually useful, but doesn't provide the URL that was contacted:

[ghost]

Another example: