refactor(effects): introduce WgslEffect for shader-only post-process effects

Replace boilerplate .h/.cc pairs for simple single-pass effects with a
generic WgslEffect base class that takes a shader string + optional
WgslEffectParams (binding 3). Port Flash, Passthrough, Heptagon, Scratch,
and GaussianBlur to thin header-only wrappers — no .cc files, no CMake
entries needed. Removes 5 .cc files (-243 lines).

Update EFFECT_WORKFLOW.md, CONTRIBUTING.md, and AI_RULES.md to document
the WgslEffect (Path A) vs full class (Path B) workflow. Doc cleanup:
fix stale GaussianBlurParams/PostProcessEffect references and test counts.

handoff(Claude): WgslEffect landed; 5 effects ported; docs updated.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 0 insertions, 60 deletions

diff --git a/src/effects/passthrough_effect.cc b/src/effects/passthrough_effect.cc
deleted file mode 100644
index 217b5d2..0000000
--- a/src/effects/passthrough_effect.cc
+++ /dev/null
@@ -1,60 +0,0 @@
-// Passthrough effect implementation
-
-#include "effects/passthrough_effect.h"
-#include "effects/shaders.h"
-#include "gpu/post_process_helper.h"
-#include "util/fatal_error.h"
-
-Passthrough::Passthrough(const GpuContext& ctx,
-                         const std::vector<std::string>& inputs,
-                         const std::vector<std::string>& outputs,
-                         float start_time, float end_time)
-    : Effect(ctx, inputs, outputs, start_time, end_time) {
-  HEADLESS_RETURN_IF_NULL(ctx_.device);
-
-  create_linear_sampler();
-
-  pipeline_.set(create_post_process_pipeline_simple(
-      ctx_.device, WGPUTextureFormat_RGBA8Unorm, passthrough_shader_wgsl));
-}
-
-void Passthrough::render(WGPUCommandEncoder encoder,
-                         const UniformsSequenceParams& params,
-                         NodeRegistry& nodes) {
-  // Get input/output views
-  WGPUTextureView input_view = nodes.get_view(input_nodes_[0]);
-  WGPUTextureView output_view = nodes.get_view(output_nodes_[0]);
-
-  // Manually create bind group with only 3 entries (no effect params needed)
-  WGPUBindGroupEntry entries[3] = {};
-  entries[0].binding = PP_BINDING_SAMPLER;
-  entries[0].sampler = sampler_.get();
-  entries[1].binding = PP_BINDING_TEXTURE;
-  entries[1].textureView = input_view;
-  entries[2].binding = PP_BINDING_UNIFORMS;
-  entries[2].buffer = uniforms_buffer_.get().buffer;
-  entries[2].size = sizeof(UniformsSequenceParams);
-
-  WGPUBindGroupDescriptor bg_desc = {};
-  bg_desc.layout = wgpuRenderPipelineGetBindGroupLayout(pipeline_.get(), 0);
-  bg_desc.entryCount = 3;
-  bg_desc.entries = entries;
-
-  bind_group_.replace(wgpuDeviceCreateBindGroup(ctx_.device, &bg_desc));
-
-  // Render pass
-  WGPURenderPassColorAttachment color_attachment = {};
-  gpu_init_color_attachment(color_attachment, output_view);
-
-  WGPURenderPassDescriptor pass_desc = {};
-  pass_desc.colorAttachmentCount = 1;
-  pass_desc.colorAttachments = &color_attachment;
-
-  WGPURenderPassEncoder pass =
-      wgpuCommandEncoderBeginRenderPass(encoder, &pass_desc);
-  wgpuRenderPassEncoderSetPipeline(pass, pipeline_.get());
-  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_.get(), 0, nullptr);
-  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0); // Fullscreen triangle
-  wgpuRenderPassEncoderEnd(pass);
-  wgpuRenderPassEncoderRelease(pass);
-}