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, 3 insertions, 0 deletions

diff --git a/src/tests/gpu/test_demo_effects.cc b/src/tests/gpu/test_demo_effects.cc
index f193c76..132e489 100644
--- a/src/tests/gpu/test_demo_effects.cc
+++ b/src/tests/gpu/test_demo_effects.cc
@@ -64,6 +64,9 @@ static void test_effects() {
       {"PeakMeter", std::make_shared<PeakMeter>(
                         fixture.ctx(), std::vector<std::string>{"source"},
                         std::vector<std::string>{"sink"}, 0.0f, 1000.0f)},
+      {"Scene1", std::make_shared<Scene1>(
+                     fixture.ctx(), std::vector<std::string>{"source"},
+                     std::vector<std::string>{"sink"}, 0.0f, 1000.0f)},
   };
 
   int passed = 0;