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, 1 insertions, 0 deletions

diff --git a/src/tests/gpu/test_demo_effects.cc b/src/tests/gpu/test_demo_effects.cc
index 4234901..ec78c10 100644
--- a/src/tests/gpu/test_demo_effects.cc
+++ b/src/tests/gpu/test_demo_effects.cc
@@ -136,6 +136,7 @@ static void test_scene_effects() {
       {"RotatingCubeEffect",
        std::make_shared<RotatingCubeEffect>(fixture.ctx())},
       {"Scene1Effect", std::make_shared<Scene1Effect>(fixture.ctx())},
+      {"SDFTestEffect", std::make_shared<SDFTestEffect>(fixture.ctx())},
   };
 
   int passed = 0;