fix(physics): L.2.3d/e/f — wall slide, edge block, step-up diagnostic

Three follow-up fixes from live testing of the L.2.3 step-height pass.

L.2.3d — StepUpSlide actually applies the slide
  Previously SpherePath.StepUpSlide only set ci.SlidingNormal as a flag and
  returned Slid; the CURRENT step's CheckPos was never adjusted, so the
  sphere stopped dead at the wall. ValidateTransition's "default to UnitZ"
  branch then propagated UnitZ into SlidingNormal, overwriting the wall
  normal entirely. Net effect: stop-at-wall, no horizontal slide.

  ACE's StepUpSlide (SpherePath.cs:309-317) calls Sphere.SlideSphere which
  computes the actual slide offset against the contact-plane / wall-normal
  crease and applies it to CheckPos. acdream already had the same logic in
  Transition.SlideSphere as a private helper. Exposed as internal
  SlideSphereInternal; routed StepUpSlide through it.

L.2.3e — step-down failure returns Collided (always-on edge block)
  When walking forward off a balcony / cliff, the step-down probe in
  TransitionalInsert searches stepDownHeight below CheckPos for a
  walkable surface. On failure the previous code returned OK, which
  ValidateTransition accepted — the player walked off the edge anyway,
  with `RestoreCheckPos` reverting only to the position right after the
  outer step's offset (still post-edge).

  Per ACE Transition.cs:268-320 (EdgeSlide), retail's always-on default
  for OnWalkable + !EdgeSlide-flag movers is to reject the move. Returning
  Collided here makes ValidateTransition revert CheckPos to CurPos
  (pre-step), giving the retail-faithful "stop at edge" behavior — both
  on terrain cliffs and on building/balcony edges.

L.2.3f — diagnostic instrumentation for steep-roof investigation
  GameWindow logs the player's actual StepUpHeight + StepDownHeight at
  world-entry (along with the raw Setup.* values for comparison) so we
  can confirm whether the dat-derived value matches retail's spec
  (~0.4m) or is overriding to something larger.

  Transition.DoStepUp logs the polygon's collision-normal Z (gated on
  ACDREAM_DUMP_STEPUP=1 to keep cold-path noise low) so we can tell
  whether step-up is being triggered against truly-walkable polygons
  (Z >= FloorZ ≈ 0.66) or whether something steeper is sneaking through.

Tests: 825/825 still pass. The L.2 conformance fixtures cover the slide
path; D1 + D2 regression tests still pass with the StepUpSlide port.

Live verification needed for:
  - #2 Wall slide: running close to a wall should slide along it.
  - #4 Edge block: running off a balcony should stop at the edge.
  - #3 Steep roof: launch with ACDREAM_DUMP_STEPUP=1 and report the
    "stepup: normal=..." log lines when climbing the offending roof.

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

src/AcDream.Core/Physics/BSPQuery.cs

@@ -1106,7 +1106,7 @@ public static class BSPQuery
         if (transition.DoStepUp(collisionNormal, engine!))
             return TransitionState.OK;
 
-        return transition.SpherePath.StepUpSlide(transition.CollisionInfo);
+        return transition.SpherePath.StepUpSlide(transition);
     }
 
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