Add-ons: Path Precision Tools — Corner Tool and Slide Anchor

Path Precision Tools gains two tools, kept out of the toolbars (All Tools
drawer and Object › Plug-ins › Path Precision Tools, no shortcuts):

- Corner Tool (cornerTool): editable corners on any path through the
  existing Live Corners. Hover shows an eligible anchor, a click cuts a
  corner with the tool's radius and kind, a drag sizes it (Shift: whole
  values), a corner's marker selects it and loads its values, resizes it
  and removes it at 0 or on a double-click; a corner never grows past
  what fits; an Alt-marquee cuts every eligible anchor inside.
- Corners section in the Anchor Inspector: radius, kind, selected count,
  Apply to Selected Anchors.
- Slide Anchor Along Path (slideAnchor): a drag runs an anchor along its
  curve, the neighbouring segments refitted by the keep-shape kernel;
  Shift snaps where the tangent is a multiple of 45° from the constrain
  angle.
- Commands addon.pathtools.cornerSet, cornerRemove and slideAnchor, one
  undo step each, params validated and covered by the command sweep.
- Cursor stand-ins, catalog rows in every language, docs and tests.

crates/pathops/src/addons/pathtools.rs

@@ -1,11 +1,13 @@
 //! Path Precision Tools' geometry: anchor edits for the Anchor Inspector (smooth by the auto-smooth
 //! rule, equalise handles, add evenly spaced anchors, close), the readouts the Measure & Inspect
-//! tool shows over a path, open paths lengthened or shortened at an end ([`extend`]) and the places
-//! where paths cross ([`crossings`]), and the Parametric Shape Tool's shapes ([`shapes`]).
+//! tool shows over a path, open paths lengthened or shortened at an end ([`extend`]), the places
+//! where paths cross ([`crossings`]), anchors slid along their path ([`slide`]) and the Parametric
+//! Shape Tool's shapes ([`shapes`]).
 
 mod crossings;
 mod extend;
 pub mod shapes;
+mod slide;
 #[cfg(test)]
 mod tests;
 
@@ -16,6 +18,7 @@ use vectorcraft_geom::{AnchorKind, PathData, SubPath};
 
 pub use crossings::{MAX_CROSSING_SEGMENTS, crossings, insert_at};
 pub use extend::{ExtendMode, extend_length_to, extend_open};
+pub use slide::{MAX_SLIDE, slide_anchor, slide_stops, slide_t_at};
 
 use crate::fit::{end_tangent, start_tangent};