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, 36 insertions, 0 deletions

diff --git a/src/effects/sdf_test_effect.cc b/src/effects/sdf_test_effect.cc
new file mode 100644
index 0000000..28b3513
--- /dev/null
+++ b/src/effects/sdf_test_effect.cc
@@ -0,0 +1,36 @@
+// This file is part of the 64k demo project.
+// It implements the SDFTestEffect.
+
+#include "effects/sdf_test_effect.h"
+#include "gpu/gpu.h"
+#include "gpu/shaders.h"
+
+SDFTestEffect::SDFTestEffect(const GpuContext& ctx) : SDFEffect(ctx) {
+  ResourceBinding bindings[] = {
+      {uniforms_.get(), WGPUBufferBindingType_Uniform},
+      {camera_params_.get(), WGPUBufferBindingType_Uniform}};
+  pass_ = gpu_create_render_pass(ctx_.device, ctx_.format,
+                                  sdf_test_shader_wgsl, bindings, 2);
+  pass_.vertex_count = 3;
+}
+
+void SDFTestEffect::render(WGPURenderPassEncoder pass,
+                           const CommonPostProcessUniforms& uniforms) {
+  // Update common uniforms
+  uniforms_.update(ctx_.queue, uniforms);
+
+  // Update camera (simple orbiting camera)
+  const float radius = 5.0f;
+  const float speed = 0.3f;
+  vec3 cam_pos(std::cos(uniforms.time * speed) * radius, 2.0f,
+               std::sin(uniforms.time * speed) * radius);
+  vec3 cam_target(0.0f, 0.0f, 0.0f);
+  vec3 cam_up(0.0f, 1.0f, 0.0f);
+  update_camera(cam_pos, cam_target, cam_up, 0.785398f, 0.1f, 100.0f,
+                uniforms.aspect_ratio);
+
+  // Render
+  wgpuRenderPassEncoderSetPipeline(pass, pass_.pipeline);
+  wgpuRenderPassEncoderSetBindGroup(pass, 0, pass_.bind_group, 0, nullptr);
+  wgpuRenderPassEncoderDraw(pass, pass_.vertex_count, 1, 0, 0);
+}