M4: vector edit transform box and point snapping (#64)

- Transform box around 2+ selected points (Move tool): corners/edges scale
  them (Shift keeps proportions, Alt from the centre), just outside a corner
  rotates them (Shift: 15° steps, the box turns with them), dragging inside
  moves them; one undo step each. Corners win over points, points over edges,
  edges over segments.
- Commands: vector.edit.bounds, vector.edit.resize, vector.edit.rotate,
  vector.edit.transform; object.flipH/V and the 90°/180° rotations act on the
  selected points while editing (unless ids are given).
- Design panel in edit mode: W/H for the selected points next to X/Y (the
  layer's dimensions are hidden while points are selected).
- Point snapping for dragged points and handles and both pens: points and
  segment midpoints of this and other vectors, the usual layer targets and
  the pixel grid, with guides and a marker on the point landed on; Ctrl/Cmd
  turns object snapping off. Snap code generalised in snap.rs (Targets spans).
- Fix: handle/bend drags read positions in the gesture snapshot's coordinates,
  so handles no longer lag when the preview re-fits the vector.
- Shared resize math (tools::resized_box) and handle hit-testing for layer
  and point boxes; canvas draws both boxes through one helper.
- Tests in vectoredit/transform_tests.rs (incl. junk sweep for the
  edit-aware commands).

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

docs/mcp.md

@@ -146,6 +146,16 @@ from the pen's open end; clicking a point connects or branches), `vector.edit.pe
 `vector.edit.cornerRadius`, `vector.edit.end`. Point indices refer to `network.vertices` in
 `vector.edit.state`; local coordinates are the layer's own.
 
+The selected points' transform box: `vector.edit.bounds` (`{x, y, width, height, corners,
+points}`: the box in the vector's axes, `x`/`y` in the parent's coordinates like the Position
+fields), `vector.edit.resize {width?, height?, center?}` (keeps the top-left unless `center`),
+`vector.edit.rotate {angle, cx?, cy?}` (degrees counter-clockwise about the box centre or a page
+pivot), `vector.edit.transform {matrix: [a, b, c, d, e, f], vertices?}` (any page-space affine).
+While points are selected, `object.flipH` / `object.flipV` and the 90°/180° rotations act on them.
+On the canvas (`pointer`), dragging points, handles and pen clicks snap to other points and segment
+midpoints (this vector's and other vectors'), the usual layer targets and the pixel grid; `cmd`
+held while dragging turns the object snapping off.
+
 Variable width strokes: `stroke.widthProfile {ids?, preset?: uniform|wedge|taper|eye|rounded|pinch,
 points?: [[t, scale], ...]}` (also `node.set {widthProfile}`; `t` runs 0–1 along each subpath by
 length, `scale` multiplies the stroke weight, widths in between are interpolated smoothly; no

docs/parity.md

@@ -1,6 +1,6 @@
 # Parity report
 
-Generated by `cargo xtask parity`: FigCraft commands registered for the incumbent's main menu and toolbar (389 commands in the engine).
+Generated by `cargo xtask parity`: FigCraft commands registered for the incumbent's main menu and toolbar (393 commands in the engine).
 
 **197 / 202 menu items (97.5%)**