feat(render): indoor render WORKS — terminating portal flood + every-cell seal + look-in FPS

Checkpoint of the unified retail-faithful indoor render. The two-week HANG/grey is fixed and the
interior seals (live-verified by the user). Commits the session render-rewrite foundation together
with the fixes that made it functional.

- HANG fix: PortalVisibilityBuilder.Build portal flood did not terminate (the faithful ProjectToClip
  near-side clip drifts per round, defeating the CellView dedup; the BFS had no bound after U.2a removed
  MaxReprocessPerCell). Fix = drift-tolerant snapped/canonical CellView.Add dedup (PortalView.cs) plus
  restored MaxReprocessPerCell=16 bounded re-enqueue (PortalVisibilityBuilder.cs). Re-enqueue is kept
  (load-bearing for late-slice propagation, Build_ViewGrowthAfterDoneCell_PropagatesNewSlicesToExit);
  only its count is capped. CellViewDedupTests added.
- Seal (DrawCells Task 2): RetailPViewRenderer.DrawEnvCellShells draws EVERY visible cell via
  IndoorDrawPlan.ShellPass (was gated on the ClipFrameAssembler slot filter, leaving slot-less cells grey).
- Look-in FPS: GameWindow exterior look-in candidates limited to the player landblock +-1 (was all ~81
  loaded LBs iterated every outdoor frame). No behaviour change (far cells were >48m, already culled).

Remaining dominant issue = the FLAP at transitions: viewer-cell metastability (render roots at the
camera-eye cell, which oscillates outdoor-indoor as the 3rd-person boom drifts across the doorway,
confirmed in render-sig). SEPARATE fix, NOT the DrawCells port. Full handoff + flap fix plan + tracked
follow-ups (#78 terrain, look-in-from-inside, look-in FPS, L-spotlight):
docs/research/2026-06-07-indoor-render-session-handoff.md.

Baselines: build 0 err; App.Tests 210/210; Core.Tests 1331 pass / 4 fail (pre-existing) / 1 skip.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/ClipPlaneSet.cs

@@ -66,7 +66,6 @@ public readonly struct ClipPlaneSet
     // or point — zero screen coverage ⇒ nothing visible. A real portal opening has area far
     // above this (e.g. the sliver-clip test region is 0.4); only an edge-on projection gets here.
     private const float MinPolygonArea = 1e-7f;
-
     private readonly Vector4[] _planes;
 
     private ClipPlaneSet(Vector4[] planes, bool useScissorFallback, bool isNothingVisible, Vector4 scissorNdcAabb)