feat(physics): [walk-miss] + [floor-polys] diagnostic emissions

Wires the WalkMissDiagnostic aggregator + flag into the two emission
sites per docs/superpowers/specs/2026-05-21-indoor-walk-miss-probe-design.md.

- [walk-miss] (per-frame, MISS branch of TryFindIndoorWalkablePlane):
  foot world+local position, nearest walkable poly with XY-containment
  flag and vertical gap, and LandCell terrain probe at the same XY.
- [floor-polys] (one-shot per cell at cache time): walkable poly id,
  normal Z, local-XY bbox, plane Z at bbox center.

Both gated on ACDREAM_PROBE_WALK_MISS=1. No physics behavior changes.
The live capture at the Holtburg cottage doorway + inn 2nd floor +
cellar descent disambiguates H1 (multi-cell iteration), H2 (probe
distance), H3 (poly absent / walkable_hits_sphere rejection) for
ISSUES #83.

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

src/AcDream.Core/Physics/PhysicsDataCache.cs

@@ -218,6 +218,24 @@ public sealed class PhysicsDataCache
             Console.WriteLine(System.FormattableString.Invariant(
                 $"[cell-cache] envCellId=0x{envCellId:X8} physicsPolyCount={cellStruct.PhysicsPolygons?.Count ?? 0} resolvedCount={resolved.Count} bspTotalLeafPolys={bspTotalLeafPolys} bspUnmatchedIds={bspUnmatchedIds} {bsStr} portalCount={portals.Count} visibleCells={visibleCellIds.Count} cellBspRoot={(cellStruct.CellBSP?.Root is null ? "null" : "ok")} worldOrigin=({worldOrigin.X:F2},{worldOrigin.Y:F2},{worldOrigin.Z:F2})"));
         }
+
+        if (PhysicsDiagnostics.ProbeWalkMissEnabled)
+        {
+            int walkableCount = 0;
+            foreach (var entry in WalkMissDiagnostic.EnumerateWalkable(
+                         resolved, PhysicsGlobals.FloorZ))
+                walkableCount++;
+
+            Console.Write(System.FormattableString.Invariant(
+                $"[floor-polys] cellId=0x{envCellId:X8} walkableCount={walkableCount}"));
+            foreach (var entry in WalkMissDiagnostic.EnumerateWalkable(
+                         resolved, PhysicsGlobals.FloorZ))
+            {
+                Console.Write(System.FormattableString.Invariant(
+                    $" [id=0x{entry.PolyId:X4} nz={entry.NormalZ:F3} bbox=({entry.BboxMin.X:F2},{entry.BboxMin.Y:F2})..({entry.BboxMax.X:F2},{entry.BboxMax.Y:F2}) planeZ@center={entry.PlaneZAtBboxCenter:F3}]"));
+            }
+            Console.WriteLine();
+        }
     }
 
     /// <summary>