remove SDFEffect base class and sdf_test, update SDF_EFFECT_GUIDE

- Delete unused SDFEffect base class (src/gpu/sdf_effect.h)
- Delete sdf_test.wgsl and SHADER_SDF_TEST from assets.txt
- Rewrite SDF_EFFECT_GUIDE.md based on Scene1 canonical pattern:
  correct bindings (2/3), vec4f syntax, UniformsSequenceParams
- Fix missing newline at end of gpu.h

handoff(Claude): SDF cleanup done, guide updated to match current Effect API

1 files changed, 1 insertions, 1 deletions

diff --git a/src/gpu/gpu.h b/src/gpu/gpu.h
index d6c0255..7754b29 100644
--- a/src/gpu/gpu.h
+++ b/src/gpu/gpu.h
@@ -104,4 +104,4 @@ WGPUSampler gpu_create_linear_sampler(WGPUDevice device);
 WGPUSampler gpu_create_nearest_sampler(WGPUDevice device);
 
 // Dummy 1x1 texture for scene effects (don't need texture input)
-TextureWithView gpu_create_dummy_scene_texture(WGPUDevice device);
\ No newline at end of file
+TextureWithView gpu_create_dummy_scene_texture(WGPUDevice device);