feat: add time-based effect activation with auto-passthrough

Effects now accept start/end time parameters and automatically passthrough
when inactive. Implements buffer chain integrity via compile-time validation.

- Effect base class: dispatch_render() checks time bounds, auto-passthroughs
  1:1 input/output effects outside [start, end] interval
- seq_compiler.py: validates producer/consumer lifespan constraints for
  multi-output effects, adds --validate flag, always validates before codegen
- Updated all 9 effect classes and test fixtures to pass start/end times
- check_all.sh: includes timeline validation step
- Tests: 34/34 passing, demo runs successfully

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

1 files changed, 2 insertions, 1 deletions

diff --git a/src/effects/hybrid3_d_effect.h b/src/effects/hybrid3_d_effect.h
index 10bee58..e0aa6da 100644
--- a/src/effects/hybrid3_d_effect.h
+++ b/src/effects/hybrid3_d_effect.h
@@ -12,7 +12,8 @@
 class Hybrid3D : public Effect {
  public:
   Hybrid3D(const GpuContext& ctx, const std::vector<std::string>& inputs,
-           const std::vector<std::string>& outputs);
+           const std::vector<std::string>& outputs, float start_time,
+               float end_time);
   ~Hybrid3D() override;
 
   void declare_nodes(NodeRegistry& registry) override;