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, 6 insertions, 12 deletions

diff --git a/src/gpu/effects/particle_spray_effect.cc b/src/gpu/effects/particle_spray_effect.cc
index a435884..9b615d0 100644
--- a/src/gpu/effects/particle_spray_effect.cc
+++ b/src/gpu/effects/particle_spray_effect.cc
@@ -27,16 +27,9 @@ ParticleSprayEffect::ParticleSprayEffect(const GpuContext& ctx) : Effect(ctx) {
   render_pass_.vertex_count = 6;
   render_pass_.instance_count = NUM_PARTICLES;
 }
-void ParticleSprayEffect::compute(WGPUCommandEncoder e, float t, float b,
-                                  float i, float a) {
-  const CommonPostProcessUniforms u = {
-      .resolution = {(float)width_, (float)height_},
-      .aspect_ratio = a,
-      .time = t,
-      .beat = b,
-      .audio_intensity = i,
-  };
-  uniforms_.update(ctx_.queue, u);
+void ParticleSprayEffect::compute(WGPUCommandEncoder e,
+                                  const CommonPostProcessUniforms& uniforms) {
+  uniforms_.update(ctx_.queue, uniforms);
   WGPUComputePassEncoder pass = wgpuCommandEncoderBeginComputePass(e, nullptr);
   wgpuComputePassEncoderSetPipeline(pass, compute_pass_.pipeline);
   wgpuComputePassEncoderSetBindGroup(pass, 0, compute_pass_.bind_group, 0,
@@ -45,8 +38,9 @@ void ParticleSprayEffect::compute(WGPUCommandEncoder e, float t, float b,
                                            1, 1);
   wgpuComputePassEncoderEnd(pass);
 }
-void ParticleSprayEffect::render(WGPURenderPassEncoder pass, float t, float b,
-                                 float i, float a) {
+void ParticleSprayEffect::render(WGPURenderPassEncoder pass,
+                                 const CommonPostProcessUniforms& uniforms) {
+  (void)uniforms;
   wgpuRenderPassEncoderSetPipeline(pass, render_pass_.pipeline);
   wgpuRenderPassEncoderSetBindGroup(pass, 0, render_pass_.bind_group, 0,
                                     nullptr);