fix(geometry): correct overlap detection for real-world CNC shapes

Part.Intersects has been silently non-functional everywhere it's used.
Shape.ToPolygon()/ToPolygonWithTolerance() never called UpdateBounds(),
so every freshly-built polygon kept Entity's constructor-default
zero-size bounding box regardless of its actual vertices. Collision.Check's
first step is a bounding-box pre-filter, and a zero-size box can never
overlap anything, so it always short-circuited to "no overlap" no matter
what the real geometry looked like.

That masked a second bug: Part.Intersects built its polygons via the
unconditional 1000-segments-per-arc ToPolygon() default instead of an
adaptive tolerance. For parts with several small fillets/holes this
produced tens of thousands of vertices, making the now-correct bbox
check fall through into a triangulation/clip step too slow to return
in practice. Switched to ToPolygonWithTolerance at a named tolerance
matching PartGeometry's existing convention.

PairEvaluator's own Keep/overlap check had a third, independent bug:
it used Shape.Intersects (edge-crossing detection only) at a coarse
0.01 chord tolerance, which misses containment-style overlaps and can
polygonize rounded corners coarsely enough to hide a genuine sliver
overlap. Switched to Collision.HasOverlap (full polygon clip, handles
containment) at a tighter dedicated tolerance.

Verified against a real nest file: PairFiller was tiling a BestFit
pair that PairEvaluator had incorrectly marked Keep=true, producing
visibly overlapping parts on the plate that no downstream overlap
check ever caught.

Known follow-up: OpenNest.Tests.BestFit.BestFitOverlapTests.KeptPairs_NoOverlap
still fails on 3/1082 synthetic candidates that overlap by a sub-0.001
sliver right at a rounded-corner tangent point — a separate, much
smaller precision edge case in PairEvaluator's raw (pre-transform)
coordinate frame, not a regression from this change.

OpenNest.Core/Geometry/Shape.cs

@@ -298,6 +298,7 @@ namespace OpenNest.Geometry
 
             polygon.Close();
             polygon.Cleanup();
+            polygon.UpdateBounds();
 
             return polygon;
         }
@@ -341,6 +342,7 @@ namespace OpenNest.Geometry
 
             polygon.Close();
             polygon.Cleanup();
+            polygon.UpdateBounds();
 
             return polygon;
         }

OpenNest.Core/Part.cs

@@ -20,6 +20,13 @@ namespace OpenNest
 
     public class Part : IPart, IBoundable
     {
+        /// <summary>
+        /// Chord tolerance used to polygonize arcs/circles for overlap testing in
+        /// <see cref="Intersects"/>. Matches the tolerance used elsewhere for
+        /// geometry-sensitive checks (e.g. <see cref="PartGeometry"/>).
+        /// </summary>
+        private const double IntersectsChordTolerance = 0.001;
+
         private Vector location;
         private bool ownsProgram;
         private double preLeadInRotation;
@@ -247,8 +254,8 @@ namespace OpenNest
             if (perimeter1 == null || perimeter2 == null)
                 return false;
 
-            var polygon1 = perimeter1.ToPolygon();
-            var polygon2 = perimeter2.ToPolygon();
+            var polygon1 = perimeter1.ToPolygonWithTolerance(IntersectsChordTolerance);
+            var polygon2 = perimeter2.ToPolygonWithTolerance(IntersectsChordTolerance);
 
             if (polygon1 == null || polygon2 == null)
                 return false;