test(render): Phase U.4 — cover ResolveEntitySlot clip-slot resolution

Code review flagged the gate-critical per-instance slot resolution as untested.
Add RED→GREEN cases (live=unclipped slot 0, cell-static→cell slot, non-visible→cull,
outdoor-stab→OutsideView/cull, routing-inactive→all slot 0). Note the full-cell-id-space
invariant at ResolveEntitySlot; fix a stale RenderInsideOut comment in EnvCellRenderer.

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

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

@@ -764,8 +764,11 @@ public sealed unsafe class EnvCellRenderer : IDisposable
     /// <summary>
     /// Draws all visible EnvCells (and their static objects) for the given pass.
     /// When <paramref name="filter"/> is non-null, only cells whose CellId is in
-    /// the set are drawn — used for indoor RenderInsideOut to restrict to camera-
-    /// building cells.
+    /// the set are drawn. As of Phase U.4 this is the portal-visibility SHELL
+    /// filter (the drawable visible cells from the PView traversal; each cell's
+    /// shell instances are clip-gated to its CellClip slot by the caller's
+    /// binding=3 map). NOTE: this is NOT the old two-pipe RenderInsideOut approach
+    /// — that flat camera-inside-building stencil pass was deleted in Phase U.1.
     /// Source: WB EnvCellRenderManager.cs:399-511 (verbatim minus selection highlights).
     /// </summary>
     public void Render(WbRenderPass renderPass, HashSet<uint>? filter)