feat(sequence): port Scene1Effect + fix seq_compiler absolute time bug

- Add Scene1 effect: raymarching cube+sphere+ground (reflections, shadows)
- Fix scene1.wgsl: binding 0→2, CommonUniforms→UniformsSequenceParams
- Replace Heptagon+Placeholder stub in heptagon_scene with Scene1
- Fix seq_compiler.py: emit seq.start_time+effect.start/end (absolute times)
  so dispatch_render active check works correctly for all sequences

Bug: effects in sequences starting after t=0 were never active because
local times (e.g. 0-8) never satisfied params.time<end for absolute time 20+.

34/34 tests passing.

handoff(Gemini): seq_compiler now emits absolute effect times. All existing
sequences affected — verify visual output across the full timeline.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/effects/scene1_effect.h b/src/effects/scene1_effect.h
new file mode 100644
index 0000000..781cbae
--- /dev/null
+++ b/src/effects/scene1_effect.h
@@ -0,0 +1,21 @@
+// Scene1 effect - raymarching cube & sphere scene
+
+#pragma once
+
+#include "gpu/effect.h"
+#include "gpu/uniform_helper.h"
+#include "gpu/wgpu_resource.h"
+
+class Scene1 : public Effect {
+ public:
+  Scene1(const GpuContext& ctx, const std::vector<std::string>& inputs,
+         const std::vector<std::string>& outputs, float start_time,
+         float end_time);
+
+  void render(WGPUCommandEncoder encoder, const UniformsSequenceParams& params,
+              NodeRegistry& nodes) override;
+
+ private:
+  RenderPipeline pipeline_;
+  BindGroup bind_group_;
+};