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, 5 insertions, 0 deletions

diff --git a/src/gpu/shaders.cc b/src/gpu/shaders.cc
index 1bf5604..30bbb0c 100644
--- a/src/gpu/shaders.cc
+++ b/src/gpu/shaders.cc
@@ -31,6 +31,7 @@ void InitShaderComposer() {
   };
 
   register_if_exists("common_uniforms", AssetId::ASSET_SHADER_COMMON_UNIFORMS);
+  register_if_exists("camera_common", AssetId::ASSET_SHADER_CAMERA_COMMON);
   register_if_exists("math/sdf_shapes", AssetId::ASSET_SHADER_MATH_SDF_SHAPES);
   register_if_exists("math/sdf_utils", AssetId::ASSET_SHADER_MATH_SDF_UTILS);
   register_if_exists("math/common_utils",
@@ -114,6 +115,10 @@ const char* scene1_shader_wgsl =
 
     SafeGetAsset(AssetId::ASSET_SHADER_SCENE1);
 
+const char* sdf_test_shader_wgsl =
+
+    SafeGetAsset(AssetId::ASSET_SHADER_SDF_TEST);
+
 const char* distort_shader_wgsl =
 
     SafeGetAsset(AssetId::ASSET_SHADER_DISTORT);