Tools: Perspective Crop (#1043) (#2864)

New Perspective Crop tool in the Crop flyout (C): drag a box or click four
corners, drag corners independently onto a skewed object, perspective grid
(Show Grid), Enter commits, Esc cancels. W/H/Resolution come from the Crop
tool's fields (Front Image, Clear), or the quad's mean side lengths.

Engine: image.perspectiveCrop {corners, width?, height?, resolution?,
interpolation?} maps the quad onto an upright canvas through the
quad-to-rectangle homography (Heckbert's square-to-quad map, inverted):
every raster layer, mask, alpha channel and the Quick Mask, one undo step.
The Background stays opaque over the background colour; type, shape, fill
and smart object layers are rasterized first; vector geometry follows the
nearest affine map. Non-convex, self-crossing, counter-clockwise or
degenerate quads are refused with an error.

algo: warp_surface_clipped bounds the per-tile warp by the new canvas even
when a layer reaches past the map's horizon; convex_quad, quad_size,
quad_to_rect.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

assets/icons/perspective-crop.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"
+>
+  <!-- PhotoCraft's own Perspective Crop tool glyph (not from an icon set): a crop frame seen in
+       perspective, with its grid and two crop-mark ticks. -->
+  <path d="M8 6h8l4 12H4z" />
+  <path d="M12 6v12" />
+  <path d="M6 12h12" />
+  <path d="M8 2v2" />
+  <path d="M20 22v-2" />
+</svg>