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, 53 insertions, 0 deletions

diff --git a/src/gpu/sdf_effect.h b/src/gpu/sdf_effect.h
new file mode 100644
index 0000000..4f23604
--- /dev/null
+++ b/src/gpu/sdf_effect.h
@@ -0,0 +1,53 @@
+// This file is part of the 64k demo project.
+// It defines SDFEffect base class for raymarching effects.
+
+#pragma once
+
+#include "3d/camera.h"
+#include "gpu/camera_params.h"
+#include "gpu/effect.h"
+#include "gpu/uniform_helper.h"
+
+// Base class for SDF raymarching effects
+// Provides CameraParams uniform buffer and helper methods
+//
+// Binding convention:
+//   @group(0) @binding(2): CommonPostProcessUniforms (from Effect base)
+//   @group(0) @binding(3): CameraParams
+//   @group(0) @binding(4+): Per-effect custom parameters
+class SDFEffect : public Effect {
+ public:
+  SDFEffect(const GpuContext& ctx) : Effect(ctx) {
+    camera_params_.init(ctx.device);
+  }
+
+  virtual ~SDFEffect() = default;
+
+  // Populate camera parameters from Camera object
+  void update_camera(const Camera& camera, float aspect_ratio) {
+    CameraParams params;
+    params.inv_view = camera.get_view_matrix().inverse();
+    params.fov = camera.fov_y_rad;
+    params.near_plane = camera.near_plane;
+    params.far_plane = camera.far_plane;
+    params.aspect_ratio = aspect_ratio;
+    camera_params_.update(ctx_.queue, params);
+  }
+
+  // Populate camera parameters with custom values
+  void update_camera(const vec3& position, const vec3& target, const vec3& up,
+                     float fov, float near_plane, float far_plane,
+                     float aspect_ratio) {
+    mat4 view = mat4::look_at(position, target, up);
+    CameraParams params;
+    params.inv_view = view.inverse();
+    params.fov = fov;
+    params.near_plane = near_plane;
+    params.far_plane = far_plane;
+    params.aspect_ratio = aspect_ratio;
+    camera_params_.update(ctx_.queue, params);
+  }
+
+ protected:
+  UniformBuffer<CameraParams> camera_params_;
+};