fix(render): interior shell and detail passes bind their own instance opacity (Campaign VM VM1)

EnvCellRenderer.Rhi's SubmitRhi bound StorageInstances/StorageBatches/
StorageClipSlots/StorageGlobalLights/StorageInstanceLightSets every frame
but never GpuBindingModel.StorageInstanceAlpha (binding 7) — the SSBO
mesh_modern.vert reads as instanceAlpha[instanceIndex] (vOpacityMultiplier,
#188) and, as of Campaign VM VM1 (05970306), mesh_detail.vert now reads the
same way (vDetailOpacity). Without a bind of its own, both the interior
shell pass and the interior detail replay read whatever section
WbDrawDispatcher's own SubmitRhi last bound in the same pass — an unrelated
object's opacity array, indexed by these EnvCell instance ids.

This predates VM1 (6c79d35c has the same omission on the mesh_modern side);
VM1 must not widen a latent defect by adding a second unconditional reader
of the same unbound slot.

Fix, root cause, no guard: EnvCellRenderer now owns _instanceAlphaData, a
grow-only float[] parallel to _gpuInstanceTransforms (same pattern as
_clipSlotData/_lightSetData), filled with the constant 1.0f every frame —
EnvCell shells have no #188 TransparentPartHook translucency fade (that
mechanism fades object PARTS, never cells) — and bound at
GpuBindingModel.StorageInstanceAlpha alongside the renderer's other
per-frame ring sections, before any draw in the pass.

Test: EnvCellRendererTests.SubmitRhi_BindsConstantOneInstanceAlphaBeforeAnyDrawInThePass
drives SubmitRhi directly (reflection, mirroring the file's existing
private-method test pattern) with N seeded cell instances and one real
draw command, then asserts against RecordingGpuDevice that
StorageInstanceAlpha is bound with exactly N floats all equal to 1.0f, and
that the bind precedes the pass's first MultiDrawIndexedIndirect call.
Verified failing (StorageInstanceAlpha was never bound) with the fix
temporarily reverted, then passing restored.

Verified: dotnet build AcDream.slnx -c Release (0 warnings, 0 errors);
dotnet test on AcDream.App.Tests (Release, hermetic lanes) green,
5960/5960 (5959 baseline + 1 new test).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -82,6 +82,18 @@ public sealed partial class EnvCellRenderer :
     // slot 0 ⇒ no-clip.
     private uint[] _clipSlotData = Array.Empty<uint>();
 
+    // Campaign VM VM1 follow-up: per-instance opacity multiplier, parallel to
+    // _gpuInstanceTransforms, feeding mesh_modern.vert/mesh_detail.vert's
+    // InstanceAlphaBuf (binding 7, GpuBindingModel.StorageInstanceAlpha).
+    // Before this field the shell and interior-detail passes never bound that
+    // storage buffer at all, so both shaders read whatever section
+    // WbDrawDispatcher's own SubmitRhi last bound in the same pass — an
+    // unrelated object's opacity array, indexed by these cell instance ids.
+    // EnvCell shells never carry a #188 TransparentPartHook translucency fade
+    // (that mechanism fades object PARTS, never cells), so every element is
+    // the constant no-op 1.0f.
+    private float[] _instanceAlphaData = Array.Empty<float>();
+
     // A7 Fix D (D-2): this renderer owns its lighting (self-contained state,
     // like uViewProjection) instead of reading whatever WbDrawDispatcher last
     // bound. Global point-light snapshot (same data/indices as the dispatcher,