feat(gpu): add SDF camera infrastructure and effect base class

Add unified camera system for SDF raymarching effects:
- CameraParams struct (80 bytes): inv_view matrix + FOV/near/far/aspect
- SDFEffect base class: manages camera uniform, provides update_camera() helpers
- camera_common.wgsl: getCameraRay(), position/forward/up/right extractors
- SDFTestEffect: working example with orbiting camera + animated sphere

Refactor effect headers:
- Extract class definitions from demo_effects.h to individual .h files
- Update includes in .cc files to use specific headers
- Cleaner compilation dependencies, faster incremental builds

Documentation:
- Add SDF_EFFECT_GUIDE.md with complete workflow
- Update ARCHITECTURE.md, UNIFORM_BUFFER_GUIDELINES.md
- Update EFFECT_WORKFLOW.md, CONTRIBUTING.md

Tests: 34/34 passing, SDFTestEffect validated

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

1 files changed, 26 insertions, 0 deletions

diff --git a/src/effects/vignette_effect.h b/src/effects/vignette_effect.h
new file mode 100644
index 0000000..f891d14
--- /dev/null
+++ b/src/effects/vignette_effect.h
@@ -0,0 +1,26 @@
+// This file is part of the 64k demo project.
+// It declares the VignetteEffect.
+
+#pragma once
+
+#include "gpu/effect.h"
+#include "gpu/uniform_helper.h"
+
+// Parameters for VignetteEffect
+struct VignetteParams {
+  float radius = 0.5f;   // Radius of the clear center
+  float softness = 0.5f; // Softness of the vignette edge
+};
+
+class VignetteEffect : public PostProcessEffect {
+ public:
+  VignetteEffect(const GpuContext& ctx);
+  VignetteEffect(const GpuContext& ctx, const VignetteParams& params);
+  void render(WGPURenderPassEncoder pass,
+              const CommonPostProcessUniforms& uniforms) override;
+  void update_bind_group(WGPUTextureView input_view) override;
+
+ private:
+  VignetteParams params_;
+  UniformBuffer<VignetteParams> params_buffer_;
+};