* feat: a custom Gradient theme with a primary and a secondary colour, picked with a wheel, sliders and a hex box
* Gradient theme: OK waits for a valid hex, deep blues are made paler, button text suits the worse gradient colour
* Gradient theme: nudge only the gradient colour that button text cannot read on
* fix: meet readable contrast across gradient themes
* fix: preserve contrast through gradient interpolation
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Co-authored-by: xXJsonDeruloXx <danielhimebauch@gmail.com>
