refactor: Factor WGPU boilerplate into builder pattern helpers

Add BindGroupLayoutBuilder, BindGroupBuilder, RenderPipelineBuilder,
and SamplerCache to reduce repetitive WGPU code. Refactor
post_process_helper, cnn_effect, and rotating_cube_effect.

Changes:
- Bind group creation: 19 instances, 14→4 lines each
- Pipeline creation: 30-50→8 lines
- Sampler deduplication: 6 instances → cached
- Total boilerplate reduction: -122 lines across 3 files

Builder pattern prevents binding index errors and consolidates
platform-specific #ifdef in fewer locations. Binary size unchanged
(6.3M debug). Tests pass.

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

1 files changed, 4 insertions, 19 deletions

diff --git a/src/gpu/effects/rotating_cube_effect.cc b/src/gpu/effects/rotating_cube_effect.cc
index 8d1f05a..da973e5 100644
--- a/src/gpu/effects/rotating_cube_effect.cc
+++ b/src/gpu/effects/rotating_cube_effect.cc
@@ -5,16 +5,14 @@
 #include "gpu/effects/rotating_cube_effect.h"
 #include "generated/assets.h"
 #include "gpu/effects/shader_composer.h"
+#include "gpu/sampler_cache.h"
 #include "util/asset_manager_utils.h"
 
 RotatingCubeEffect::RotatingCubeEffect(const GpuContext& ctx) : Effect(ctx) {
 }
 
 RotatingCubeEffect::~RotatingCubeEffect() {
-  if (mask_sampler_)
-    wgpuSamplerRelease(mask_sampler_);
-  if (noise_sampler_)
-    wgpuSamplerRelease(noise_sampler_);
+  // Samplers owned by SamplerCache - don't release
   if (noise_view_)
     wgpuTextureViewRelease(noise_view_);
   if (noise_texture_)
@@ -49,21 +47,8 @@ void RotatingCubeEffect::init(MainSequence* demo) {
   noise_texture_ = wgpuDeviceCreateTexture(ctx_.device, &tex_desc);
   noise_view_ = wgpuTextureCreateView(noise_texture_, nullptr);
 
-  WGPUSamplerDescriptor sampler_desc = {};
-  sampler_desc.addressModeU = WGPUAddressMode_Repeat;
-  sampler_desc.addressModeV = WGPUAddressMode_Repeat;
-  sampler_desc.magFilter = WGPUFilterMode_Linear;
-  sampler_desc.minFilter = WGPUFilterMode_Linear;
-  sampler_desc.maxAnisotropy = 1;
-  noise_sampler_ = wgpuDeviceCreateSampler(ctx_.device, &sampler_desc);
-
-  WGPUSamplerDescriptor mask_sampler_desc = {};
-  mask_sampler_desc.addressModeU = WGPUAddressMode_ClampToEdge;
-  mask_sampler_desc.addressModeV = WGPUAddressMode_ClampToEdge;
-  mask_sampler_desc.magFilter = WGPUFilterMode_Linear;
-  mask_sampler_desc.minFilter = WGPUFilterMode_Linear;
-  mask_sampler_desc.maxAnisotropy = 1;
-  mask_sampler_ = wgpuDeviceCreateSampler(ctx_.device, &mask_sampler_desc);
+  noise_sampler_ = SamplerCache::Get().get_or_create(ctx_.device, SamplerCache::linear());
+  mask_sampler_ = SamplerCache::Get().get_or_create(ctx_.device, SamplerCache::clamp());
 
   size_t shader_size;
   const char* shader_code =