feat(lighting): SelectForCell (all dynamic lights per EnvCell) + #176 handoff — residual is a runtime z-fight

cdb trace of LIVE retail (tools/cdb/issue176-floor-light.cdb, binary<->PDB MATCH) PROVED retail
applies ALL its dynamic lights — 4 intensity-100 magenta portal lights (d3dIdx 3-6, falloff 6) +
the viewer fill (d3dIdx 1, 2.25) — as D3D hardware lights to EVERY Facility Hub cell, every frame,
stable. So the faceted purple wedges on the floor are retail-FAITHFUL. acdream did a per-cell
SelectForObject sphere-overlap 8-cap for cells, so the portal set could differ/flip per cell.

- LightManager.SelectForCell (retail minimize_envcell_lighting 0x0054c170): ALL dynamic lights
  applied unconditionally (shader range cutoff zeroes non-reaching = D3D hardware range), then
  nearest static torches fill remaining slots. Wired into EnvCellRenderer.GetCellLightSet.
  Objects keep SelectForObject (minimize_object_lighting). Pins:
  SelectForCell_AppliesAllDynamicLights_EvenOutOfReach + _SameDynamicSet_ForCellsFarApart_NoFlap.
- Apparatus: [light-detail] gains owner/cell/dyn (pinned the culprit = 2 portal weenies
  0x000F4247/48 in 0x8A020118/19, intensity=100 magenta); CellVertexNormals_SmoothOrFaceted_Dump
  (corridor floor uses SMOOTH per-vertex dat normals, not flat); tools/cdb/issue176-floor-light.cdb.

#176 RESIDUAL is NOT this fix. It's a RUNTIME draw z-fight in the seam floor. Eliminated (evidence):
NOT lighting (per-light cap + this both no-change), NOT membership (render cell 0x8A020164 stable
100% of 188k frames / 526 angles, res=None), NOT dat geometry (coplanar sweep empty at z=-6 floor
incl. cell 0164). NEXT = RenderDoc pixel-history. Full handoff + DO-NOT-RETRY:
docs/research/2026-07-06-176-seam-floor-zfight-handoff.md. Suites green: Core 2599 + 2 skip.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/AcDream.App/Rendering/Wb/EnvCellRenderer.cs

@@ -1085,7 +1085,10 @@ public sealed unsafe class EnvCellRenderer : IDisposable
         {
             Vector3 center = (b.Min + b.Max) * 0.5f;
             float radius = (b.Max - b.Min).Length() * 0.5f;
-            AcDream.Core.Lighting.LightManager.SelectForObject(snap, center, radius, set);
+            // #176 flap fix: cells use SelectForCell (retail minimize_envcell_lighting) — ALL
+            // dynamic lights on every cell (stable), not the per-object sphere-overlap cull that
+            // let the portal set flip as the flood shifted → floor-lighting flap.
+            AcDream.Core.Lighting.LightManager.SelectForCell(snap, center, radius, set);
         }
         _cellLightSetCache[cellId] = set;
         return set;