Properties: Curves adjustment layers get the black/gray/white eyedroppers (#3110) (#3115)

* Curves: pencil mode, Smooth and Edit points (#3088)

The Curves editor (Image > Adjustments dialog and the adjustment layer's
Properties panel) gains Photoshop's "Edit points to modify the curve" and
"Draw to modify the curve" buttons plus Smooth, with tooltips. A drawn
curve is a 256-level map per channel, evaluated piecewise-linearly.

- doc: Adjustment::Curves gains `pencil` (serde default), with
  curve_map / curve_map_outputs helpers.
- compose: curve_map_lut / curve_lut_mode for drawn curves.
- engine: curves params take `pencil` and `smooth`; channels accept
  256-level maps; switching modes draws the spline into maps or fits up to
  16 points to the drawing. Eyedroppers fit points first.
- io: the PSD `curv` map flag (first byte, psd-tools `is_map`) was read
  as padding, so pencil curves from Photoshop were misparsed; they are now
  read and written as 256-byte maps, and smart-filter Curves use `Mpng`.
- scorecard UI-217-15 note updated.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Properties: Curves adjustment layers get the black/gray/white eyedroppers (#3110)

The Set Black/Neutral Gray/White Point pickers existed only in the
Image > Adjustments > Curves dialog (#873). The Properties editor of a
Curves adjustment layer now has them too (layer_picker.rs): with one
armed, a click on the image runs one layer.setAdjustment with the new
`eyedropper` param, which samples the image below the layer (the layer
hidden, like its Properties histogram) at the Eyedropper's Sample Size,
so a repeated click keeps the curve and the edit is one undoable,
recordable step agents can send directly. Esc, another tool or another
layer disarms it; ui.pointer and ui.inspect (`layerPicker`) cover it.

Scorecard UI-217-15 is done.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Merge upstream/main: Curves in new compose/gpu HDR tests gets the pencil field (#3088)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>

scorecard/ui.toml

@@ -106,9 +106,9 @@ note = "panels.rs: the wheel steps the blend-mode dropdown (widgets::dropdown_wh
 [[item]]
 id = "UI-217-15"
 target = "Curves: smoothing / pencil mode, black/grey/white eyedroppers, tooltips"
-status = "partial"
+status = "done"
 issue = 217
-note = "Curves editor (adjust_editors.rs, dialog and Properties): Edit points / Draw (pencil) buttons and Smooth, all with tooltips; pencil curves are 256-level maps (Adjustment::Curves pencil, params pencil/smooth, PSD curv map form and smart-filter Mpng; #3088). The Image > Adjustments > Curves dialog has the black/gray/white eyedroppers (adjust_dialog.rs, #873); the adjustment layer's Properties panel has none yet"
+note = "Curves editor (adjust_editors.rs, dialog and Properties): Edit points / Draw (pencil) buttons and Smooth, all with tooltips; pencil curves are 256-level maps (Adjustment::Curves pencil, params pencil/smooth, PSD curv map form and smart-filter Mpng; #3088). Set Black/Neutral Gray/White Point eyedroppers in the Image > Adjustments > Curves dialog (adjust_dialog.rs, #873) and in a Curves adjustment layer's Properties panel (layer_picker.rs: a click on the image is one layer.setAdjustment with the eyedropper param, sampling below the layer; Esc or another tool disarms; #3110)"
 
 [[item]]
 id = "UI-217-16"