refactor(cnn): isolate CNN v2 to cnn_v2/ subdirectory

Move all CNN v2 files to dedicated cnn_v2/ directory to prepare for CNN v3 development. Zero functional changes.

Structure:
- cnn_v2/src/ - C++ effect implementation
- cnn_v2/shaders/ - WGSL shaders (6 files)
- cnn_v2/weights/ - Binary weights (3 files)
- cnn_v2/training/ - Python training scripts (4 files)
- cnn_v2/scripts/ - Shell scripts (train_cnn_v2_full.sh)
- cnn_v2/tools/ - Validation tools (HTML)
- cnn_v2/docs/ - Documentation (4 markdown files)

Changes:
- Update CMake source list to cnn_v2/src/cnn_v2_effect.cc
- Update assets.txt with relative paths to cnn_v2/
- Update includes to ../../cnn_v2/src/cnn_v2_effect.h
- Add PROJECT_ROOT resolution to Python/shell scripts
- Update doc references in HOWTO.md, TODO.md
- Add cnn_v2/README.md

Verification: 34/34 tests passing, demo runs correctly.

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

1 files changed, 89 insertions, 0 deletions

diff --git a/cnn_v2/src/cnn_v2_effect.h b/cnn_v2/src/cnn_v2_effect.h
new file mode 100644
index 0000000..7960b4f
--- /dev/null
+++ b/cnn_v2/src/cnn_v2_effect.h
@@ -0,0 +1,89 @@
+// CNN v2 Effect - Parametric Static Features
+// Multi-pass post-processing with 7D feature input
+// Supports per-layer kernel sizes (e.g., 1×1, 3×3, 5×5)
+
+#pragma once
+#include "gpu/effect.h"
+#include <vector>
+
+struct CNNv2EffectParams {
+  float blend_amount = 1.0f;
+};
+
+class CNNv2Effect : public PostProcessEffect {
+ public:
+  explicit CNNv2Effect(const GpuContext& ctx);
+  explicit CNNv2Effect(const GpuContext& ctx, const CNNv2EffectParams& params);
+  ~CNNv2Effect();
+
+  void init(MainSequence* demo) override;
+  void resize(int width, int height) override;
+  void compute(WGPUCommandEncoder encoder,
+               const CommonPostProcessUniforms& uniforms) override;
+  void render(WGPURenderPassEncoder pass,
+              const CommonPostProcessUniforms& uniforms) override;
+  void update_bind_group(WGPUTextureView input_view) override;
+
+  void set_beat_modulation(bool enabled, float scale = 1.0f) {
+    beat_modulated_ = enabled;
+    beat_scale_ = scale;
+  }
+
+ private:
+  struct LayerInfo {
+    uint32_t kernel_size;
+    uint32_t in_channels;
+    uint32_t out_channels;
+    uint32_t weight_offset;
+    uint32_t weight_count;
+  };
+
+  struct LayerParams {
+    uint32_t kernel_size;
+    uint32_t in_channels;
+    uint32_t out_channels;
+    uint32_t weight_offset;
+    uint32_t is_output_layer;
+    float blend_amount;
+    uint32_t is_layer_0;
+  };
+
+  struct StaticFeatureParams {
+    uint32_t mip_level;
+    uint32_t padding[3];
+  };
+
+  void create_textures();
+  void create_pipelines();
+  void load_weights();
+  void cleanup();
+
+  // Static features compute
+  WGPUComputePipeline static_pipeline_;
+  WGPUBindGroup static_bind_group_;
+  WGPUBuffer static_params_buffer_;
+  WGPUTexture static_features_tex_;
+  WGPUTextureView static_features_view_;
+  WGPUSampler linear_sampler_;
+
+  // CNN layers (storage buffer architecture)
+  WGPUComputePipeline layer_pipeline_; // Single pipeline for all layers
+  WGPUBuffer weights_buffer_;          // Storage buffer for weights
+  std::vector<WGPUBuffer>
+      layer_params_buffers_;          // Uniform buffers (one per layer)
+  std::vector<LayerInfo> layer_info_; // Layer metadata
+  std::vector<WGPUBindGroup> layer_bind_groups_; // Per-layer bind groups
+  std::vector<WGPUTexture> layer_textures_;      // Ping-pong buffers
+  std::vector<WGPUTextureView> layer_views_;
+
+  // Input mips
+  WGPUTexture input_mip_tex_;
+  WGPUTextureView input_mip_view_[3];
+  WGPUTextureView current_input_view_;
+
+  float blend_amount_ = 1.0f;
+  bool beat_modulated_ = false;
+  float beat_scale_ = 1.0f;
+  uint32_t mip_level_ = 0;
+  bool initialized_;
+};