Redesign color picker sidebar

- Consolidate header buttons (eyedropper/lock/reset/close) into one icon row
- Inline contrast as a single line under hex input
- Add copy-hex button using shared copyColor()
- Replace the 4-row ShadeGrid with a 2D saturation x lightness tone grid
  plus a 12-step hue rainbow strip
- Swap local ratio() for the existing contrastRatio() utility
- Make hexInput validation a $derived; consolidate ANSI-edit guards into
  a single isAnsi flag
- Hoist the dynamic Wails import and add a stale-resolve token guard for
  ComputeVariables

Author: bjarneo