feat(sequence): port rotating_cube_effect to v2

- Add RotatingCubeEffectV2 with 3D rendering + depth buffer
- Create rotating_cube_v2.wgsl (hardcoded cube geometry)
- Simplified: no auxiliary mask texture dependency
- Declare depth node via NodeRegistry
- Update timeline_v2.seq rotating_cube sequence
- Add shader exports to shaders.{h,cc}
- All 36 tests passing

handoff(Claude): RotatingCube v2 complete, hybrid_3d next

1 files changed, 49 insertions, 0 deletions

diff --git a/src/effects/rotating_cube_effect_v2.h b/src/effects/rotating_cube_effect_v2.h
new file mode 100644
index 0000000..19ef410
--- /dev/null
+++ b/src/effects/rotating_cube_effect_v2.h
@@ -0,0 +1,49 @@
+// This file is part of the 64k demo project.
+// It declares RotatingCubeEffectV2 (simplified v2 port).
+
+#pragma once
+
+#include "gpu/effect_v2.h"
+#include "gpu/gpu.h"
+#include "gpu/uniform_helper.h"
+#include "util/mini_math.h"
+
+class RotatingCubeEffectV2 : public EffectV2 {
+ public:
+  RotatingCubeEffectV2(const GpuContext& ctx,
+                       const std::vector<std::string>& inputs,
+                       const std::vector<std::string>& outputs);
+  ~RotatingCubeEffectV2() override;
+
+  void declare_nodes(NodeRegistry& registry) override;
+  void render(WGPUCommandEncoder encoder,
+              const UniformsSequenceParams& params,
+              NodeRegistry& nodes) override;
+
+ private:
+  struct Uniforms {
+    mat4 view_proj;
+    mat4 inv_view_proj;
+    vec4 camera_pos_time;
+    vec4 params;
+    vec2 resolution;
+    float aspect_ratio;
+    float _pad;
+  };
+  static_assert(sizeof(Uniforms) == 176, "Uniforms size mismatch");
+
+  struct ObjectData {
+    mat4 model;
+    mat4 inv_model;
+    vec4 color;
+    vec4 params;
+  };
+  static_assert(sizeof(ObjectData) == 160, "ObjectData size mismatch");
+
+  WGPURenderPipeline pipeline_ = nullptr;
+  WGPUBindGroup bind_group_ = nullptr;
+  GpuBuffer uniform_buffer_;
+  GpuBuffer object_buffer_;
+  float rotation_ = 0.0f;
+  std::string depth_node_;
+};