refactor: Simplify effect render API and fix uniform initialization

Root cause: Uniform buffers created but not initialized before bind group
creation, causing undefined UV coordinates in circle_mask_compute.wgsl.

Changes:
- Add get_common_uniforms() helper to Effect base class
- Refactor render()/compute() signatures: 5 params → CommonPostProcessUniforms&
- Fix uninitialized uniforms in CircleMaskEffect and CNNEffect
- Update all 19 effect implementations and headers
- Fix WGSL syntax error in FlashEffect (u.audio_intensity → audio_intensity)
- Update test files (test_sequence.cc)

Benefits:
- Cleaner API: construct uniforms once per frame, reuse across effects
- More maintainable: CommonPostProcessUniforms changes need no call site updates
- Fixes UV coordinate bug in circle_mask_compute.wgsl

All 36 tests passing (100%)

handoff(Claude): Effect API refactor complete

1 files changed, 1 insertions, 8 deletions

diff --git a/src/gpu/effects/passthrough_effect.cc b/src/gpu/effects/passthrough_effect.cc
index 01d557a..aedb387 100644
--- a/src/gpu/effects/passthrough_effect.cc
+++ b/src/gpu/effects/passthrough_effect.cc
@@ -11,14 +11,7 @@ PassthroughEffect::PassthroughEffect(const GpuContext& ctx)
                                            passthrough_shader_wgsl);
 }
 void PassthroughEffect::update_bind_group(WGPUTextureView input_view) {
-  const CommonPostProcessUniforms u = {
-      .resolution = {(float)width_, (float)height_},
-      .aspect_ratio = 1.0f,
-      .time = 0.0f,
-      .beat = 0.0f,
-      .audio_intensity = 0.0f,
-  };
-  uniforms_.update(ctx_.queue, u);
+  uniforms_.update(ctx_.queue, get_common_uniforms());
   pp_update_bind_group(ctx_.device, pipeline_, &bind_group_, input_view,
                        uniforms_.get(), {});
 }