[css-color-4] Add sample pseudocode for the EdgeSeeker gamut mapping algorithm - #14426

…algorithm

Binary Search and Ray Trace already had pseudocode; EdgeSeeker only had
prose. Add pseudocode for LUT construction, curvature calculation, and
the per-color mapping steps, derived from the color.js reference
implementation.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Fixes errors in the EdgeSeeker pseudocode found by checking it against
the reference implementation and by numerical testing against a
bisection ground truth.

- Key LUT entries by the OkLCh hue of the sampled color, not by the HSL
  hue used to generate it. The two differ by up to 50deg in sRGB, so the
  LUT was misindexed; RMS error against ground truth was 0.0475, with a
  peak overestimate of +0.21 chroma, which left the residual clip doing
  essentially all the work. This also reconciles the pseudocode with the
  existing note about hue non-monotonicity, which can only arise under
  OkLCh-hue keying.
- Interpolate the curve point at the cusp's hue rather than pairing it
  with the cusp sampled from the same HSL hue; the two lightnesses give
  OkLCh hues up to 16deg apart. Matches getColor() in makeLut.js.
- Sample each 60deg hue region separately, so the six primaries and
  secondaries are sampled exactly, and clarify that N is per region.
- Add the wrap-around entries at 0deg and 360deg, so every hue is
  bracketed, and normalize hue before lookup, since OkLCh hue in CSS is
  not restricted to a single turn.
- Correct the direction of x in the arc intersection: it is 1 at the
  cusp and 0 at white, not the reverse. State the normalization
  convention where the curvature is derived.
- Handle a missing (powerless) hue.
- Use the sRGB LUT for HSL and HWB destinations.

After these corrections, RMS error against ground truth is 0.00014 for
sRGB and 0.00017 for display-p3, with a peak residual of 0.004 chroma,
comfortably handled by the final clip.

Also autolink the four new dfns instead of bolding them, fix the
colorjs-EdgeSeeker href, which had moved to gamut-mapping/methods/,
and fix "less than than" and a missing </li>.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>