Sketch constraints accept x / y for the sketch's own axes (#394) (#448)

`sketch.constraint.symmetry` (line), `parallel`, `perpendicular`,
`collinear`, `tangent` and `coincident` (point on curve) now take `x` /
`y` for the sketch's own axes, matching what `solid.revolve` means by
lowercase x|y. A real curve with that id still wins.

An axis becomes a linked construction line on it: a new
`LinkSource::SketchAxis` resolved in sketch coordinates, so it stays on
the sketch's axis on any plane, is shared by every constraint on that
axis, is left out of profiles and is reported in `created`. Equal,
concentric, midpoint and horizontal/vertical keep refusing axes, since
the axis line's finite length or fixed direction would make them
meaningless.


Claude-Session: https://claude.ai/code/session_01YDDPmNdRoBgkHcLeUDKVfb

Co-authored-by: Claude Opus 5.5 <[email protected]>

crates/doc/src/project.rs

@@ -259,6 +259,9 @@ fn resolve_uncached(
                 _ => vec![LinkGeom::Point(o)],
             }
         }
+        LinkSource::SketchAxis { name } => {
+            vec![solidcraft_sketch::sketch_axis_geom(name).ok_or_else(|| DocError::Unknown(format!("sketch axis `{name}`")))?]
+        }
         LinkSource::Text { text, at, height, angle } => solidcraft_sketch::text_geometry(text, *at, *height, *angle)?,
         LinkSource::Plane { name } => {
             let pr =