Upgrade to Storybook v8 & fix flaky UI tests

[winston]

1. upgrade to Storybook v8.
2. get rid of React dependencies. react -> webcomponents
3. use a subset of JetBrains Mono instead of the whole package (this should fix flaky fonts)
   

   vscode/packages/catppuccin-vsc-storybook/.storybook/preview.ts

   Line 3 in d7b96cc

    import "@fontsource-variable/jetbrains-mono";