feat(core): Phase B.3 — CellPortal-based indoor/outdoor transitions in PhysicsEngine

Replace the disabled if(false) outdoor→indoor branch with real portal-plane
crossing logic. LandblockPhysics now carries IReadOnlyList<PortalPlane> Portals
(populated at load time; GameWindow passes Array.Empty for now until Task 3).

Resolve logic:
- Outdoor player: tests all portals where TargetCellId==0xFFFF (outside-facing);
  crossing enters the portal's OwnerCellId.
- Indoor player: tests portals where OwnerCellId==currentCell; crossing to
  TargetCellId==0xFFFF exits to terrain, otherwise transitions room-to-room.
- Landblock boundary crossing: unchanged — candidatePos landblock lookup already
  picks the adjacent block's terrain naturally.

Tests: renamed disabled test → Resolve_OutdoorThroughPortal_TransitionsToIndoor;
added Resolve_IndoorThroughExitPortal_TransitionsToOutdoor and
Resolve_LandblockBoundary_PicksAdjacentTerrain. 274 tests green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -1367,7 +1367,8 @@ public sealed class GameWindow : IDisposable
                 }
             }
 
-            _physicsEngine.AddLandblock(lb.LandblockId, terrainSurface, cellSurfaces, origin.X, origin.Y);
+            _physicsEngine.AddLandblock(lb.LandblockId, terrainSurface, cellSurfaces,
+                Array.Empty<AcDream.Core.Physics.PortalPlane>(), origin.X, origin.Y);
         }
 
         // Upload every GfxObj referenced by this landblock's entities.
@@ -1496,7 +1497,8 @@ public sealed class GameWindow : IDisposable
                 TurnLeft:    kb.IsKeyPressed(Key.A),
                 TurnRight:   kb.IsKeyPressed(Key.D),
                 Run:         kb.IsKeyPressed(Key.ShiftLeft) || kb.IsKeyPressed(Key.ShiftRight),
-                MouseDeltaX: consumedMouseDeltaX);
+                MouseDeltaX: consumedMouseDeltaX,
+                Jump:        kb.IsKeyPressed(Key.Space));
 
             var result = _playerController.Update((float)dt, input);