M8.12: Perspective Selection tool scales, copies, moves perpendicular and nudges in perspective

The Perspective Selection tool shows the selection's bounding box in perspective; its handles
scale in plane space (perspective.transform; Shift proportional, Alt from the centre). Alt-drag
moves copies that stay attached, pressing 5 while dragging moves along the plane's normal
(ToolKey::Digit, delivered by the canvas and MCP press_key), and the arrow keys nudge in
perspective (perspective.nudge). Transform Again repeats the last perspective move or scale in
plane space. Attachments (plane and depth) now live on the objects (Node.perspective), so copies,
duplicates and pastes keep them; grids from older files hand theirs over. Homography moves to
vectorcraft-geom. Hint-bar text for the tool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/doc/src/node.rs

@@ -343,6 +343,9 @@ pub struct Node {
     /// [`crate::orient`]); Reset Bounding Box sets it back to 0.
     #[serde(default, skip_serializing_if = "crate::skip::is_default")]
     pub bbox_angle: f64,
+    /// Object › Perspective: the perspective grid plane the object is attached to.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub perspective: Option<Box<crate::PerspectiveAttachment>>,
 }
 
 /// Opacity mask: the luminance of the mask art sets the object's opacity (white = opaque).
@@ -392,6 +395,7 @@ impl Node {
             attrs: None,
             slice: None,
             bbox_angle: 0.0,
+            perspective: None,
         }
     }
     pub fn path(id: NodeId, path: PathData, appearance: Appearance) -> Self {