fix(physics): Slice 1 — delete render-mesh-AABB synthetic collision; DAT-only shape authority

Retail oracle: CPartArray::InitParts@0x00517F40, CGfxObj::Serialize@0x00534970 (physics_bsp
gated on serialized-flags bit-0), CPhysicsPart::find_obj_collisions@0x0050D8D0 (returns OK /
passable when physics_bsp==null). Render-mesh bounds never enter collision.

Changes:
- GameWindow.cs: delete the ~200-line VISUAL mesh-bounds collision block (the
  isPhantomSetup / isPhantomGfxObj locals + the if-block computing worldMin/worldMax
  AABB + the ShadowObjects.Register call that capped and registered the synthetic
  cylinder). Also removes dead counter variables scHaveBounds/scRegistered/scNoBounds/
  scTooThin; trims the ProbeBuildingEnabled summary line accordingly.
- PhysicsDataCache.cs: delete IsPhantomGfxObjSource (the predicate that only existed
  to fence the mesh-AABB synthesis; the "phantom" concept is now the default — no DAT
  shape means no registration, verbatim with retail).
- PhysicsDataCachePhantomSourceTests.cs: deleted (tested the removed method).
- ShadowShapeBuilderShapeSourceTests.cs: new guard test — a Setup with parts but
  hasPhysicsBsp=false and no CylSpheres/Spheres yields an empty shape list, locking
  the DAT-only rule in the builder.
- retail-divergence-register.md: AP-2 row deleted (divergence retired).

Objects with no DAT physics shape (no CylSpheres, no Spheres, no part with a
PhysicsBSP) now register no collision shape and are passable, verbatim with retail.
Objects with real DAT shapes (BSP parts, CylSpheres) are unaffected.

dotnet build green, 22/22 tests passing (ShadowShapeBuilderShapeSourceTests +
CellarUpTrajectoryReplay + CornerFlood + Issue147ArwicBuildings replay harnesses).

Visual gate pending: walk Holtburg + open world; objects that become passable must
match retail (DAT has no physics shape — trees with real CylSpheres still solid).

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

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

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using AcDream.Core.Physics;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Enums;
+using DatReaderWriter.Types;
+using Xunit;
+
+namespace AcDream.Core.Tests.Physics;
+
+/// <summary>
+/// Guards the DAT-only shape-source rule (Slice 1 of the unified
+/// collision-inclusion phase, 2026-06-24).
+///
+/// <para>
+/// Retail oracle: <c>CPartArray::InitParts@0x00517F40</c> (parts come from
+/// the Setup list only), <c>CGfxObj::Serialize@0x00534970</c> (physics_bsp
+/// gated on serialized-flags bit-0), <c>CPhysicsPart::find_obj_collisions@0x0050D8D0</c>
+/// (returns OK / passable when <c>physics_bsp == null</c>). Render-mesh bounds
+/// never enter collision.
+/// </para>
+/// </summary>
+public class ShadowShapeBuilderShapeSourceTests
+{
+    // Retail: an object with no DAT physics shape (no CylSphere, no Sphere,
+    // no part with a PhysicsBSP) emits NO collision shape and is passable.
+    // CPhysicsPart::find_obj_collisions@0x0050D8D0 returns OK when physics_bsp==null.
+    [Fact]
+    public void Setup_WithNoCylSpheres_NoSpheres_NoPhysicsBspParts_YieldsEmptyShapeList()
+    {
+        var setup = new Setup
+        {
+            CylSpheres      = new List<CylSphere>(),
+            Spheres         = new List<Sphere>(),
+            Parts           = { 0x01000ABCu },
+            PlacementFrames = new Dictionary<Placement, AnimationFrame>(),
+        };
+        var shapes = ShadowShapeBuilder.FromSetup(setup, entScale: 1f, hasPhysicsBsp: _ => false);
+        Assert.Empty(shapes);
+    }
+}