perf(theme): drop the redundant acrylic grain under glass cards

Glass cards draw their own grain layer over the surface overlay, but the
acrylic primitive beneath them was also drawing its grain. That lower
layer sits under the overlay at well below one grey level, so it is
invisible and only costs an extra noise pass per card.

- The card now asks the acrylic primitive for zero grain and keeps its
  own visible grain layer, removing the redundant pass with no visible
  change.

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

src/ui/material/draw_helpers.h

@@ -741,9 +741,11 @@ inline void DrawGlassPanel(ImDrawList* dl, const ImVec2& pMin,
         // (skip the blur pass at 100% for performance)
         if (uiOp < 0.99f) {
             if (useAcrylic) {
-                const auto& acrylicTheme = GetCurrentAcrylicTheme();
-                effects::ImGuiAcrylic::DrawAcrylicRect(dl, pMin, pMax,
-                                                       acrylicTheme.card, spec.rounding);
+                // The card draws its own grain layer below (noise B, over the surface overlay), so skip
+                // the acrylic primitive's grain here: it sits under the overlay at < 1 grey level.
+                effects::AcrylicParams cardParams = GetCurrentAcrylicTheme().card;
+                cardParams.noiseOpacity = 0.0f;
+                effects::ImGuiAcrylic::DrawAcrylicRect(dl, pMin, pMax, cardParams, spec.rounding);
             } else {
                 // Lightweight fake-glass: translucent fill
                 ImU32 fill = (spec.fillAlpha == 18) ? s_glassFill : ScaleAlpha(s_glassFill, spec.fillAlpha / 18.0f);