feat(sequence): complete phase 3 - v2 shader integration and effect ports

- Create v2-compatible WGSL shaders with UniformsSequenceParams
- Add sequence_v2_uniforms snippet for ShaderComposer
- Port 3 effects: PassthroughEffectV2, GaussianBlurEffectV2, HeptagonEffectV2
- Enable and fix end-to-end test (test_sequence_v2_e2e)
- Fix shader binding order (sampler at 0, texture at 1)
- Fix WebGPU validation (maxAnisotropy=1, explicit depthSlice)
- Add v2 shaders to main and test workspace assets
- All tests passing (36/36)

handoff(Claude): Phase 3 complete, v2 effects functional, ready for phase 4

4 files changed, 21 insertions, 30 deletions

diff --git a/src/effects/gaussian_blur_effect_v2.cc b/src/effects/gaussian_blur_effect_v2.cc
index 6b37f0b..f87de8b 100644
--- a/src/effects/gaussian_blur_effect_v2.cc
+++ b/src/effects/gaussian_blur_effect_v2.cc
@@ -11,7 +11,7 @@ GaussianBlurEffectV2::GaussianBlurEffectV2(const GpuContext& ctx,
       sampler_(nullptr) {
   // Create pipeline
   pipeline_ = create_post_process_pipeline(ctx_.device, WGPUTextureFormat_RGBA8Unorm,
-                                           gaussian_blur_shader_wgsl);
+                                           gaussian_blur_v2_shader_wgsl);
 
   // Create sampler
   WGPUSamplerDescriptor sampler_desc = {};
@@ -19,6 +19,7 @@ GaussianBlurEffectV2::GaussianBlurEffectV2(const GpuContext& ctx,
   sampler_desc.addressModeV = WGPUAddressMode_ClampToEdge;
   sampler_desc.magFilter = WGPUFilterMode_Linear;
   sampler_desc.minFilter = WGPUFilterMode_Linear;
+  sampler_desc.maxAnisotropy = 1;
   sampler_ = wgpuDeviceCreateSampler(ctx_.device, &sampler_desc);
 
   // Init uniform buffers
diff --git a/src/effects/heptagon_effect_v2.cc b/src/effects/heptagon_effect_v2.cc
index 4478327..3512ec7 100644
--- a/src/effects/heptagon_effect_v2.cc
+++ b/src/effects/heptagon_effect_v2.cc
@@ -14,7 +14,7 @@ HeptagonEffectV2::HeptagonEffectV2(const GpuContext& ctx,
   // Create render pass using helper
   ResourceBinding bindings[] = {{uniforms_buffer_.get(), WGPUBufferBindingType_Uniform}};
   RenderPass pass = gpu_create_render_pass(ctx_.device, WGPUTextureFormat_RGBA8Unorm,
-                                          main_shader_wgsl, bindings, 1);
+                                          heptagon_v2_shader_wgsl, bindings, 1);
   pipeline_ = pass.pipeline;
   bind_group_ = pass.bind_group;
 }
diff --git a/src/effects/passthrough_effect_v2.cc b/src/effects/passthrough_effect_v2.cc
index d98315f..5203f97 100644
--- a/src/effects/passthrough_effect_v2.cc
+++ b/src/effects/passthrough_effect_v2.cc
@@ -9,9 +9,11 @@ PassthroughEffectV2::PassthroughEffectV2(const GpuContext& ctx,
                                          const std::vector<std::string>& outputs)
     : EffectV2(ctx, inputs, outputs), pipeline_(nullptr), bind_group_(nullptr),
       sampler_(nullptr) {
+  // Init uniform buffer
+  uniforms_buffer_.init(ctx_.device);
   // Create pipeline
   pipeline_ = create_post_process_pipeline(ctx_.device, WGPUTextureFormat_RGBA8Unorm,
-                                           passthrough_shader_wgsl);
+                                           passthrough_v2_shader_wgsl);
 
   // Create sampler
   WGPUSamplerDescriptor sampler_desc = {};
@@ -21,6 +23,7 @@ PassthroughEffectV2::PassthroughEffectV2(const GpuContext& ctx,
   sampler_desc.magFilter = WGPUFilterMode_Linear;
   sampler_desc.minFilter = WGPUFilterMode_Linear;
   sampler_desc.mipmapFilter = WGPUMipmapFilterMode_Nearest;
+  sampler_desc.maxAnisotropy = 1;
   sampler_ = wgpuDeviceCreateSampler(ctx_.device, &sampler_desc);
 }
 
@@ -31,36 +34,21 @@ void PassthroughEffectV2::render(WGPUCommandEncoder encoder,
   WGPUTextureView input_view = nodes.get_view(input_nodes_[0]);
   WGPUTextureView output_view = nodes.get_view(output_nodes_[0]);
 
-  // Update bind group (recreate each frame for simplicity)
-  WGPUBindGroupEntry entries[3] = {};
+  // Update uniforms
+  uniforms_buffer_.update(ctx_.queue, params);
 
-  entries[0].binding = PP_BINDING_SAMPLER;
-  entries[0].sampler = sampler_;
-
-  entries[1].binding = PP_BINDING_TEXTURE;
-  entries[1].textureView = input_view;
-
-  // Uniforms (binding 2) - use empty buffer for now
-  entries[2].binding = PP_BINDING_UNIFORMS;
-  entries[2].buffer = nullptr;
-  entries[2].size = 0;
-
-  WGPUBindGroupDescriptor bg_desc = {};
-  bg_desc.layout = wgpuRenderPipelineGetBindGroupLayout(pipeline_, 0);
-  bg_desc.entryCount = 2;  // Only sampler and texture, no uniforms
-  bg_desc.entries = entries;
-
-  if (bind_group_) {
-    wgpuBindGroupRelease(bind_group_);
-  }
-  bind_group_ = wgpuDeviceCreateBindGroup(ctx_.device, &bg_desc);
+  // Update bind group using helper (handles dummy buffers)
+  pp_update_bind_group(ctx_.device, pipeline_, &bind_group_, input_view,
+                       uniforms_buffer_.get(), {nullptr, 0});
 
   // Render pass
-  WGPURenderPassColorAttachment color_attachment = {};
-  color_attachment.view = output_view;
-  color_attachment.loadOp = WGPULoadOp_Clear;
-  color_attachment.storeOp = WGPUStoreOp_Store;
-  color_attachment.clearValue = {0.0, 0.0, 0.0, 1.0};
+  WGPURenderPassColorAttachment color_attachment = {
+    .view = output_view,
+    .depthSlice = WGPU_DEPTH_SLICE_UNDEFINED,
+    .loadOp = WGPULoadOp_Clear,
+    .storeOp = WGPUStoreOp_Store,
+    .clearValue = {0.0, 0.0, 0.0, 1.0}
+  };
 
   WGPURenderPassDescriptor pass_desc = {};
   pass_desc.colorAttachmentCount = 1;
diff --git a/src/effects/passthrough_effect_v2.h b/src/effects/passthrough_effect_v2.h
index 813361e..a272b87 100644
--- a/src/effects/passthrough_effect_v2.h
+++ b/src/effects/passthrough_effect_v2.h
@@ -3,6 +3,7 @@
 #pragma once
 
 #include "gpu/effect_v2.h"
+#include "gpu/uniform_helper.h"
 
 class PassthroughEffectV2 : public EffectV2 {
  public:
@@ -16,4 +17,5 @@ class PassthroughEffectV2 : public EffectV2 {
   WGPURenderPipeline pipeline_;
   WGPUBindGroup bind_group_;
   WGPUSampler sampler_;
+  UniformBuffer<UniformsSequenceParams> uniforms_buffer_;
 };