Merge p10-w1-renderer-swap into dev (Phase 10 Wave 1: WebGL2 fragment-shader Mix renderer at parity)

DeepDrftPublic.Client/Controls/MixWaveformVisualizer.razor.css

@@ -8,17 +8,16 @@
     overflow: hidden;
 }
 
-/* The canvas fills the viewport. The glassy/frosted treatment is a CSS backdrop-blur on this layer
-   (the ribbon's luminous depth is drawn inside the canvas by the module); together they read as lit
-   glass moving behind the content rather than a hard chart. */
+/* The canvas fills the viewport. All ribbon shading (luminous depth, soft edges) is drawn inside the
+   canvas by the WebGL2 fragment shader. NO CSS backdrop-filter: it was a confirmed per-frame perf killer
+   on the Canvas predecessor and is exactly the cost the GPU move exists to eliminate (spec §2, §5.2);
+   the glass treatment returns in-shader in Wave 3. */
 .mix-waveform-canvas {
     position: absolute;
     inset: 0;
     width: 100%;
     height: 100%;
     display: block;
-    backdrop-filter: blur(2px);
-    -webkit-backdrop-filter: blur(2px);
 }
 
 /* Zoom slider — a small viewing control pinned to the top-right, clear of the player bar at