Part of #394: Preferences that act on selection, the wheel, tool tips and the grid

Fifteen Preferences options were stored but read by nothing. They now act,
through the existing plumbing (ToolContext for the tools, the prefs read by the
canvas for the view), and reach agents through prefs.set:

- General: Show Tool Tips (off: no widget's tool tip comes due), Double Click
  To Isolate, Zoom with Mouse Wheel (the wheel zooms about the pointer,
  Shift-wheel scrolls up and down, Cmd/Ctrl-wheel sideways), Use Precise
  Cursors (Pen, Eyedropper, Slice and Blend pointers become a crosshair).
- Selection & Anchor Display: Tolerance (objects, anchors and handles, in
  place of the fixed 3 and 4 px), Object Selection by Path Only (compound
  paths too), Command Click to Select Objects Behind (cycles down the objects
  under the pointer; not when Cmd only borrows the selection tool), Zoom to
  Selection (Zoom In/Out centre the selection), anchor Size, Highlight anchors
  on mouse over (Direct Selection).
- Type: Number of Recent Fonts (up to 15 Recent Fonts slots).
- Guides & Grid: guide and grid Color and Style (lines or dots), Grids In Back.

The canvas's context menu, panel drops and hover highlight pick objects like
the selection tools. The control channel gets ui.wheel (with modifiers held
like ui.click) so agents can turn the wheel. The rest of #394 stays open.

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

crates/tools/src/select.rs

@@ -1,13 +1,14 @@
 //! The Selection tool (V): click/shift-click, marquee, move (Alt copies, Shift constrains),
 //! bounding-box scale (Shift proportional, Alt from centre) and rotate (outside corners, Shift 45°),
 //! drag a live rectangle's corner widget to round its corners (Alt-click cycles their kind,
-//! double-click opens the Corners dialog), double-click to enter isolation mode.
+//! double-click opens the Corners dialog), double-click to enter isolation mode (Double Click To
+//! Isolate), Cmd/Ctrl-click to select the object behind (Command Click to Select Objects Behind).
 //! The bounding box stands at the selection's own angle after a rotation, so its handles scale
 //! along the objects' axes. A handle drag resizes area type's frame (the type area) instead of
 //! scaling its type: the text reflows at its size.
 
 use serde_json::{Value, json};
-use vectorcraft_doc::hit::{hit_test, marquee};
+use vectorcraft_doc::hit::{hit_test, marquee, objects_at};
 use vectorcraft_doc::{NodeId, OrientedBox};
 use vectorcraft_geom::{Affine, Point, Rect};
 
@@ -114,7 +115,7 @@ impl Tool for SelectionTool {
                 }
                 if let Some(h) = hit_test(cx.doc, p, cx.hit_options()) {
                     let top = h.top_object(cx.isolation);
-                    if cx.doc.node(top).is_some_and(|n| matches!(n.kind, vectorcraft_doc::NodeKind::Group { .. })) {
+                    if cx.double_click_isolate && cx.doc.node(top).is_some_and(|n| matches!(n.kind, vectorcraft_doc::NodeKind::Group { .. })) {
                         return vec![Action::Exec("object.isolate".into(), json!({ "id": top.0 }))];
                     }
                     if cx.doc.node(top).is_some_and(|n| matches!(n.kind, vectorcraft_doc::NodeKind::Text(_))) {
@@ -152,7 +153,14 @@ impl Tool for SelectionTool {
                         None => {}
                     }
                 }
-                // 2. Objects.
+                // 2. Objects: Cmd/Ctrl-click selects the one under the selected one (cycling).
+                if m.cmd
+                    && cx.select_behind
+                    && let Some(behind) = object_behind(cx, p)
+                {
+                    self.state = State::Moving { start: p, began: false, deselect: None };
+                    return vec![Action::Exec("select.set".into(), json!({ "ids": [behind.0] }))];
+                }
                 match hit_test(cx.doc, p, cx.hit_options()) {
                     Some(h) => {
                         let top = h.top_object(cx.isolation);
@@ -321,6 +329,14 @@ impl Tool for SelectionTool {
     }
 }
 
+/// Select Behind: of the objects under `p` (topmost first), the one below the lowest selected
+/// one, back to the topmost after the bottom one; the topmost when none is selected.
+fn object_behind(cx: &ToolContext, p: Point) -> Option<NodeId> {
+    let stack = objects_at(cx.doc, p, cx.hit_options(), cx.isolation);
+    let next = stack.iter().rposition(|id| cx.selection.contains(*id)).map_or(0, |i| i + 1);
+    stack.get(next).or(stack.first()).copied()
+}
+
 /// Is `n` area type (text in a frame) whose frame the tools reshape? Type in perspective isn't:
 /// it transforms whole.
 pub(crate) fn is_area_type(n: &vectorcraft_doc::Node) -> bool {