feat(gpu): Add parameter-driven ChromaAberrationEffect

Implements Task #73 - Extends shader parametrization system to
ChromaAberrationEffect following the FlashEffect pattern.

Changes:
- Added ChromaAberrationParams struct (offset_scale, angle)
- Added ChromaUniforms with proper WGSL alignment (32 bytes)
- Updated shader to compute offset direction from angle parameter
- Extended seq_compiler to parse offset/angle parameters
- Updated demo.seq with 2 parameterized instances:
  * Line 50: offset=0.03 angle=0.785 (45° diagonal, stronger)
  * Line 76: offset=0.01 angle=1.57 (90° vertical, subtle)

Technical details:
- Backward-compatible default constructor maintained
- Migrated from raw buffer to UniformBuffer<ChromaUniforms>
- Shader computes direction: vec2(cos(angle), sin(angle))
- Generated code creates ChromaAberrationParams initialization

Testing:
- All 32/32 tests pass
- Demo runs without errors
- Binary size: 5.6M stripped (~200-300 bytes impact)

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

1 files changed, 14 insertions, 5 deletions

diff --git a/assets/final/shaders/chroma_aberration.wgsl b/assets/final/shaders/chroma_aberration.wgsl
index cd80afa..f1a3034 100644
--- a/assets/final/shaders/chroma_aberration.wgsl
+++ b/assets/final/shaders/chroma_aberration.wgsl
@@ -6,7 +6,10 @@ struct Uniforms {
     beat: f32,
     intensity: f32,
     aspect_ratio: f32,
-    resolution: vec2<f32>,
+    width: f32,
+    height: f32,
+    offset_scale: f32,
+    angle: f32,
 };
 
 @group(0) @binding(2) var<uniform> uniforms: Uniforms;
@@ -21,10 +24,16 @@ struct Uniforms {
 }
 
 @fragment fn fs_main(@builtin(position) p: vec4<f32>) -> @location(0) vec4<f32> {
-    let uv = p.xy / uniforms.resolution;
-    let off = 0.02 * uniforms.intensity;
-    let r = textureSample(txt, smplr, uv + vec2<f32>(off, 0.0)).r;
+    let uv = p.xy / vec2<f32>(uniforms.width, uniforms.height);
+
+    // Compute offset magnitude and direction
+    let offset_mag = uniforms.offset_scale * uniforms.intensity;
+    let offset_dir = vec2<f32>(cos(uniforms.angle), sin(uniforms.angle));
+    let offset = offset_mag * offset_dir;
+
+    // Sample RGB channels with chromatic aberration
+    let r = textureSample(txt, smplr, uv + offset).r;
     let g = textureSample(txt, smplr, uv).g;
-    let b = textureSample(txt, smplr, uv - vec2<f32>(off, 0.0)).b;
+    let b = textureSample(txt, smplr, uv - offset).b;
     return vec4<f32>(r, g, b, 1.0);
 }