Sketch: accept redundant but consistent constraints (#687) (#699)

A clover of same-size rectangles drawn around a shared corner was refused as over-constrained.

Constraints that remove no degree of freedom but still hold (zero residual) are now kept and shown dimmed as redundant. Conflicting ones are still refused. A redundant driving dimension is refused with "already determined by ...". Typed sizes become driven (reference) dimensions. Drawing no longer adds Horizontal/Vertical to a side that is already implied through two coincident corners. The solver reports redundant constraints using a Jacobian row-dependence test.

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

crates/engine/src/cmd/sketch_axis_ref_tests.rs

@@ -232,7 +232,8 @@ fn bad_line_references_are_errors_and_change_nothing() {
     // A constraint the sketch refuses rolls the axis line back with it.
     run(&mut s, "sketch.constraint.horizontal_vertical", json!({"line": "b", "mode": "horizontal"}));
     let before_redundant = s.doc.to_json();
-    assert!(s.execute("sketch.constraint.parallel", &json!({"a": "b", "b": "x"})).is_err(), "already horizontal");
+    // (A redundant one is kept unless refused: refused here.)
+    assert!(s.execute("sketch.constraint.parallel", &json!({"a": "b", "b": "x", "if_redundant": "refuse"})).is_err(), "already horizontal");
     assert_eq!(s.doc.to_json(), before_redundant);
     assert!(axis_lines(&sketch(&s)).is_empty());
 }