Tools: Freeform Pen and Curvature Pen (#1054) (#2856)

The Pen flyout (P / Shift+P) now holds Pen, Freeform Pen and Curvature Pen.

Freeform Pen: a drag draws freehand; on release the trace is fitted with
cubic Beziers within the options bar's Curve Fit (default 2 px) by
photocraft_vector::trace::fit_trace (Schneider, "An Algorithm for
Automatically Fitting Digitized Curves", Graphics Gems 1990, the fitting
Make Work Path already uses), keeping turns sharper than 60 degrees as
corners. Releasing on the start point closes the path.

Curvature Pen: each click adds a smooth point and the path runs through
every point (Catmull-Rom style handles from
photocraft_vector::edit::curvature_knots); dragging a point moves it,
double-clicking toggles corner/smooth, clicking the first point closes,
Enter/Esc finish and Backspace removes the last point, as with the Pen.

Both commit through the Pen's path: a shape layer in Shape mode, else the
targeted vector mask, else the work path, as one History step.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

README.md

@@ -133,7 +133,7 @@ Every screenshot here is the real app at work on public-domain art, rendered off
       <br>
       <sub>A badge made of shape layers: a gradient-filled lotus, a star and a dotted ring.<br><i>Water Lilies</i>, Claude Monet, 1906</sub>
       <h3>Pixel-perfect vectors</h3>
-      Rectangle, Ellipse, Triangle, Polygon, Line and the Pen tool, with resolution-independent shape layers, gradient fills, and dashed, aligned strokes.
+      Rectangle, Ellipse, Triangle, Polygon, Line and the Pen, Freeform Pen and Curvature Pen tools, with resolution-independent shape layers, gradient fills, and dashed, aligned strokes.
       <br><br>
       Combine shapes (unite, subtract, intersect, exclude), keep paths in the Paths panel, use them as vector masks, or stroke and fill them. 116 of 116 shape layers in our PSD corpus match Photoshop's pixels.
     </td>
@@ -178,8 +178,8 @@ Every screenshot here is the real app at work on public-domain art, rendered off
 <table>
   <tr>
     <td width="33%" valign="top">
-      <h4>🧰 58 tools</h4>
-      Move · Rectangular and Elliptical Marquee · Single Row Marquee · Single Column Marquee · Lasso · Polygonal Lasso · Magnetic Lasso · Object Selection · Quick Selection · Magic Wand · Crop · Slice · Slice Select · Eyedropper · Ruler · Note · Count · Remove · Spot Healing Brush · Healing Brush · Patch · Content-Aware Move · Red Eye · Brush · Pencil · Mixer Brush · Color Replacement · Clone Stamp · Pattern Stamp · History Brush · Eraser · Background Eraser · Magic Eraser · Gradient · Paint Bucket · Blur · Sharpen · Smudge · Dodge · Burn · Sponge · Pen · Add Anchor Point · Delete Anchor Point · Horizontal and Vertical Type · Path Selection · Direct Selection · Rectangle · Ellipse · Triangle · Polygon · Line · Custom Shape · Hand · Rotate View · Zoom
+      <h4>🧰 60 tools</h4>
+      Move · Rectangular and Elliptical Marquee · Single Row Marquee · Single Column Marquee · Lasso · Polygonal Lasso · Magnetic Lasso · Object Selection · Quick Selection · Magic Wand · Crop · Slice · Slice Select · Eyedropper · Ruler · Note · Count · Remove · Spot Healing Brush · Healing Brush · Patch · Content-Aware Move · Red Eye · Brush · Pencil · Mixer Brush · Color Replacement · Clone Stamp · Pattern Stamp · History Brush · Eraser · Background Eraser · Magic Eraser · Gradient · Paint Bucket · Blur · Sharpen · Smudge · Dodge · Burn · Sponge · Pen · Freeform Pen · Curvature Pen · Add Anchor Point · Delete Anchor Point · Horizontal and Vertical Type · Path Selection · Direct Selection · Rectangle · Ellipse · Triangle · Polygon · Line · Custom Shape · Hand · Rotate View · Zoom
     </td>
     <td width="33%" valign="top">
       <h4>🖌️ A real brush engine</h4>