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>

assets/icons/pen-curvature.svg

@@ -0,0 +1,21 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <g transform="translate(7 7) scale(0.68)" stroke-width="2.6">
+    <path d="M15.707 21.293a1 1 0 0 1-1.414 0l-1.586-1.586a1 1 0 0 1 0-1.414l5.586-5.586a1 1 0 0 1 1.414 0l1.586 1.586a1 1 0 0 1 0 1.414z" />
+    <path d="m18 13-1.375-6.874a1 1 0 0 0-.746-.776L3.235 2.028a1 1 0 0 0-1.207 1.207L5.35 15.879a1 1 0 0 0 .776.746L13 18" />
+    <path d="m2.3 2.3 7.286 7.286" />
+    <circle cx="11" cy="11" r="2" />
+  </g>
+  <path d="M3 12C3 7 7 3 12 3" />
+  <circle cx="3" cy="12" r="1" fill="currentColor" />
+  <circle cx="12" cy="3" r="1" fill="currentColor" />
+</svg>

assets/icons/pen-freeform.svg

@@ -0,0 +1,19 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <g transform="translate(7 7) scale(0.68)" stroke-width="2.6">
+    <path d="M15.707 21.293a1 1 0 0 1-1.414 0l-1.586-1.586a1 1 0 0 1 0-1.414l5.586-5.586a1 1 0 0 1 1.414 0l1.586 1.586a1 1 0 0 1 0 1.414z" />
+    <path d="m18 13-1.375-6.874a1 1 0 0 0-.746-.776L3.235 2.028a1 1 0 0 0-1.207 1.207L5.35 15.879a1 1 0 0 0 .776.746L13 18" />
+    <path d="m2.3 2.3 7.286 7.286" />
+    <circle cx="11" cy="11" r="2" />
+  </g>
+  <path d="M8.5 8.5C6 6 7.5 3 5 3S2 6 4 7.5 5.5 11 3 12" />
+</svg>