fix(node colours): Revisit the colour theming for nodes

[simonwinter]

Summary

Currently we're relying on very generic tailwind colours to set our node background colours etc.

const nodeColours = (name: string) => ({
  colour: colours[name][100],
  borderColour: colours[name][200],
})

In general, the design requires more variation than this. We need to review the available design tokens.

Examples:

Note: I think there may be some colour mistakes here - black for block heading, incorrect purple on icon when not needed.

[nokome]

Yes, agreed. Someone needs to go through and finish populating the nodeTypeUIMap with specific colour and borderColour hex (?) colours. The nodeColours func was just an expedient gap filler until the final colors were chosen in the Figma designs.

Having said that, I'm not sure we have final colour choices and there are some inconsistencies in the latest designs (e.g. CodeChunk is a green, whereas its inline equivalent, a CodeExpression is a blue). So as part of this lets review all the colors used.