feat(sequence): port particles_effect to v2

- Add ParticlesEffectV2 with compute + render passes
- Create particle_compute_v2.wgsl and particle_render_v2.wgsl
- Use UniformsSequenceParams for beat-synchronized particles
- Update timeline_v2.seq particles sequence (simplified 2-effect chain)
- Add shader exports to shaders.{h,cc}
- All 36 tests passing

handoff(Claude): Particles v2 complete, rotating_cube next

1 files changed, 31 insertions, 0 deletions

diff --git a/workspaces/main/shaders/particle_compute_v2.wgsl b/workspaces/main/shaders/particle_compute_v2.wgsl
new file mode 100644
index 0000000..3683826
--- /dev/null
+++ b/workspaces/main/shaders/particle_compute_v2.wgsl
@@ -0,0 +1,31 @@
+// Particle simulation (compute shader) - V2
+struct Particle {
+    pos: vec4<f32>,
+    vel: vec4<f32>,
+    rot: vec4<f32>,
+    color: vec4<f32>,
+};
+
+#include "sequence_v2_uniforms"
+
+@group(0) @binding(0) var<storage, read_write> particles: array<Particle>;
+@group(0) @binding(1) var<uniform> uniforms: UniformsSequenceParams;
+
+@compute @workgroup_size(64)
+fn main(@builtin(global_invocation_id) id: vec3<u32>) {
+    let i = id.x;
+    if (i >= arrayLength(&particles)) {
+        return;
+    }
+    var p = particles[i];
+    let new_pos = p.pos.xyz + p.vel.xyz * 0.016;
+    p.pos = vec4<f32>(new_pos, p.pos.w);
+    p.vel.y = p.vel.y - 0.01 * (1.0 + uniforms.audio_intensity * 5.0);
+    p.rot.x = p.rot.x + p.rot.y * 0.016;
+    if (p.pos.y < -1.5) {
+        p.pos.y = 1.5;
+        p.pos.x = (f32(i % 100u) / 50.0) - 1.0 + (uniforms.audio_intensity * 0.5);
+        p.vel.y = 0.0;
+    }
+    particles[i] = p;
+}