test_demo: Add beat-synchronized CNN post-processing with version selection

- Add --cnn-version <1|2> flag to select between CNN v1 and v2
- Implement beat_phase modulation for dynamic blend in both CNN effects
- Fix CNN v2 per-layer uniform buffer sharing (each layer needs own buffer)
- Fix CNN v2 y-axis orientation to match render pass convention
- Add Scene1Effect as base visual layer to test_demo timeline
- Reorganize CNN v2 shaders into cnn_v2/ subdirectory
- Update asset paths and documentation for new shader organization

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/gpu/effects/cnn_effect.cc b/src/gpu/effects/cnn_effect.cc
index b2305b2..83a3365 100644
--- a/src/gpu/effects/cnn_effect.cc
+++ b/src/gpu/effects/cnn_effect.cc
@@ -79,12 +79,19 @@ void CNNEffect::resize(int width, int height) {
 
 void CNNEffect::render(WGPURenderPassEncoder pass,
                       const CommonPostProcessUniforms& uniforms) {
-  (void)uniforms;
   if (!bind_group_) {
     fprintf(stderr, "CNN render: no bind_group\n");
     return;
   }
 
+  float effective_blend = blend_amount_;
+  if (beat_modulated_) {
+    effective_blend = blend_amount_ * uniforms.beat_phase * beat_scale_;
+  }
+
+  CNNLayerParams params = {layer_index_, effective_blend, {0.0f, 0.0f}};
+  params_buffer_.update(ctx_.queue, params);
+
   wgpuRenderPassEncoderSetPipeline(pass, pipeline_);
   wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_, 0, nullptr);
   wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);