phase(N.1): delete legacy scenery code path; WB is the only path

Phase N.1 step 8 (final code cleanup): now that ACDREAM_USE_WB_SCENERY
has been default-on (commit b84ecbd), remove the legacy in-line
algorithms so we don't accumulate dead-code drift.

Deleted:
- SceneryGenerator.UseWbScenery (feature flag)
- SceneryGenerator.IsOnRoad / DisplaceObject / RoadHalfWidth (legacy
  ports — Generate used to call them)
- The legacy in-line implementation in Generate()
- SceneryGeneratorTests.DisplaceObject_* (test the deleted method)
- SceneryWbConformanceTests.cs entirely (purpose served — proved
  equivalence pre-migration; would compare WB to WB after delete)

Renamed:
- GenerateViaWb -> GenerateInternal (it's the only path now)

Kept:
- Public IsRoadVertex predicate (small surface, useful)
- WbSceneryAdapter (consumed by GenerateInternal)
- All WbSceneryAdapterTests (still cover the adapter)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/World/SceneryGeneratorTests.cs

@@ -1,13 +1,14 @@
-using System.Numerics;
 using AcDream.Core.World;
 using DatReaderWriter.Types;
 
 namespace AcDream.Core.Tests.World;
 
 /// <summary>
-/// Tests for SceneryGenerator: road-exclusion, loop bounds, building
-/// suppression, and slope filter. The full Generate() pipeline requires
-/// real dat files so behavior is tested via internal helpers.
+/// Tests for SceneryGenerator. As of Phase N.1 (commit b84ecbd / Task 8 final
+/// commit), the displacement / road / slope / rotation / scale algorithms run
+/// through WorldBuilder's helpers (SceneryHelpers + TerrainUtils). The only
+/// our-side code remaining is the small <see cref="SceneryGenerator.IsRoadVertex"/>
+/// predicate, which is what these tests cover.
 /// </summary>
 public class SceneryGeneratorTests
 {
@@ -47,63 +48,4 @@ public class SceneryGeneratorTests
                 $"raw=0x{raw:X4}: IsRoadVertex={actual} but TerrainInfo.Road={ti.Road}");
         }
     }
-
-    // --- Edge vertex displacement tests ---
-    // Retail iterates 9×9 vertices (0..8 on each axis). Vertices at x=8 or y=8
-    // have base positions at 192 (= 8 * 24), which is AT the landblock boundary.
-    // These produce valid scenery when displacement shifts them back into [0, 192).
-
-    [Fact]
-    public void DisplaceObject_EdgeVertex_CanProduceValidPosition()
-    {
-        // Vertex (3, 8): base_y = 8 * 24 = 192.
-        // With DisplaceY > 0, some LCG seeds will produce negative displacement,
-        // shifting the Y back below 192 into the valid range.
-        var obj = new ObjectDesc
-        {
-            DisplaceX = 12f,
-            DisplaceY = 12f,
-            BaseLoc = new Frame { Origin = new Vector3(0, 0, 0) }
-        };
-
-        // Search across a range of global cell coords to find at least one
-        // case where vertex y=8 displaces into [0, 192).
-        bool foundValid = false;
-        for (uint gx = 0; gx < 64 && !foundValid; gx++)
-        {
-            for (uint gy = 0; gy < 64 && !foundValid; gy++)
-            {
-                var localPos = SceneryGenerator.DisplaceObject(obj, gx, gy, 0);
-                // Vertex (3, 8): cell corner at (3*24, 8*24) = (72, 192)
-                float lx = 3 * 24f + localPos.X;
-                float ly = 8 * 24f + localPos.Y;
-                if (ly >= 0 && ly < 192f && lx >= 0 && lx < 192f)
-                    foundValid = true;
-            }
-        }
-
-        Assert.True(foundValid,
-            "Expected at least one (globalCellX, globalCellY) where vertex y=8 " +
-            "displaces back into [0, 192) — retail's 9×9 loop relies on this");
-    }
-
-    [Fact]
-    public void DisplaceObject_InteriorVertex_AlwaysNearOrigin()
-    {
-        var obj = new ObjectDesc
-        {
-            DisplaceX = 12f,
-            DisplaceY = 12f,
-            BaseLoc = new Frame { Origin = new Vector3(0, 0, 0) }
-        };
-
-        // For interior vertices (x < 8, y < 8), displacement is bounded by
-        // DisplaceX/Y (max 12 units each), so the result stays within one
-        // cell of the origin.
-        var localPos = SceneryGenerator.DisplaceObject(obj, 100, 100, 0);
-        Assert.True(Math.Abs(localPos.X) <= 12f,
-            $"Interior displacement X={localPos.X} exceeds DisplaceX=12");
-        Assert.True(Math.Abs(localPos.Y) <= 12f,
-            $"Interior displacement Y={localPos.Y} exceeds DisplaceY=12");
-    }
 }