Specbook 0.8.1: APIs that allow CORS work again with the extension installed

With the 0.8.0 extension installed, a live call to an API that already allows CORS (the Petstore demo, for example) asked you to allow it first. It no longer does.

• A call to an API you have not allowed yet is tried straight from the page first, as it was before the extension. Only when the browser blocks that does the response offer Allow. The one exception is a plain POST (a form or text body, no headers of its own), which a browser sends without asking the API first, so it still asks you first.
• The extension's window is readable in dark mode: failed rows in "Recent calls" are now a lighter red.

The extension zip (specbook-extension-chromium-0.8.1.zip) changes only in that dark-mode color; the call fix is in @specbook/ui.

No breaking changes.

Full Changelog: v0.8.0...v0.8.1