feat(physics): Task 2 — true sphere collision primitive (CSphere::intersects_sphere)

Setup.Spheres were previously coerced to short cylinders (CylHeight=2*r),
which is geometrically wrong: a cylinder has flat caps; a sphere does not.
This ported CSphere::intersects_sphere (0x00537A80) so sphere-typed shadow
entries are tested as spheres — 3-D distance, no height clamping.

Changes:
- ShadowObjectRegistry.cs: added ShadowCollisionType.Sphere (enum value 2).
  The BuildFloodSpheres anyCyl dedup at :232 is unaffected: only Cylinder
  sets anyCyl=true; Sphere shapes fall through to the BSP-fallback path
  (anyCyl=false → included), which is correct.
- ShadowShapeBuilder.cs: FromSetup now emits ShadowCollisionType.Sphere
  (CylHeight=0) for Setup.Spheres instead of a short Cylinder.
- CollisionPrimitives.cs: added SweptSphereHitsSphere — quadratic swept
  solve ported from ACE Sphere.cs::FindTimeOfCollision, which is a C# port
  of retail's CSphere::intersects_sphere @ 0x00537A80. Sign convention
  confirmed against the decomp: retail negates the root to produce a
  forward t ∈ (0,1].
- TransitionTypes.cs: added Sphere narrow-phase branch between BSP and
  Cylinder in FindObjCollisionsInCell; uses 3-D distance for overlap
  (not XY-only). Added SphereCollision() method implementing the 3-D
  wall-slide response. Updated diagnostic logging at :2734 to cover Sphere.
- Updated ShadowShapeBuilderTests for new Sphere type assertion.
- New SphereIntersectsSphereConformanceTests: 9 geometrically-anchored
  cases (head-on, tangent, perpendicular-miss, lateral-near-miss,
  sweep-away, beyond-step, degenerate-zero-sweep, already-overlapping,
  vertical-sweep).

Retail oracle: CSphere::intersects_sphere @ 0x00537A80 (named-retail);
ACE Sphere.cs::FindTimeOfCollision (C# port, cross-confirmed).
Build: 0 errors, 10 warnings (pre-existing).
Tests: 1576 pass / 0 fail / 2 skip (1578 total).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Physics/ShadowShapeBuilderTests.cs

@@ -57,14 +57,17 @@ public class ShadowShapeBuilderTests
 
         Assert.Equal(4, shapes.Count);
 
-        int cylinderCount = 0;
+        // Task 2 (2026-06-24): Setup.Spheres now emit ShadowCollisionType.Sphere,
+        // not Cylinder.  A door's Sphere entry contributes the Sphere-typed shape;
+        // the 3 parts (all with physics BSP) contribute the 3 BSP shapes.
+        int sphereCount = 0;
         int bspCount = 0;
         foreach (var s in shapes)
         {
-            if (s.CollisionType == ShadowCollisionType.Cylinder) cylinderCount++;
+            if (s.CollisionType == ShadowCollisionType.Sphere) sphereCount++;
             else if (s.CollisionType == ShadowCollisionType.BSP) bspCount++;
         }
-        Assert.Equal(1, cylinderCount);
+        Assert.Equal(1, sphereCount);
         Assert.Equal(3, bspCount);
     }
 
@@ -74,12 +77,16 @@ public class ShadowShapeBuilderTests
         var setup = CreateDoorSetup();
         var shapes = ShadowShapeBuilder.FromSetup(setup, 1.0f, _ => true);
 
-        var sphereAsCyl = shapes.FirstOrDefault(s => s.CollisionType == ShadowCollisionType.Cylinder);
-        Assert.NotEqual(default, sphereAsCyl);
-        Assert.Equal(0f, sphereAsCyl.LocalPosition.X, 4);
-        Assert.Equal(0f, sphereAsCyl.LocalPosition.Y, 4);
-        Assert.Equal(0.018f, sphereAsCyl.LocalPosition.Z, 4);
-        Assert.Equal(0.100f, sphereAsCyl.Radius, 4);
+        // Task 2 (2026-06-24): Spheres emit ShadowCollisionType.Sphere (not Cylinder).
+        // Retail: CSphere::intersects_sphere @ 0x00537A80 uses 3-D distance; no height cap.
+        var sphereShape = shapes.FirstOrDefault(s => s.CollisionType == ShadowCollisionType.Sphere);
+        Assert.NotEqual(default, sphereShape);
+        Assert.Equal(0f,     sphereShape.LocalPosition.X, 4);
+        Assert.Equal(0f,     sphereShape.LocalPosition.Y, 4);
+        Assert.Equal(0.018f, sphereShape.LocalPosition.Z, 4);
+        Assert.Equal(0.100f, sphereShape.Radius, 4);
+        // CylHeight must be 0 — spheres have no height cap.
+        Assert.Equal(0f, sphereShape.CylHeight, 4);
     }
 
     [Fact]