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, 6 insertions, 2 deletions

diff --git a/doc/EFFECT_WORKFLOW.md b/doc/EFFECT_WORKFLOW.md
index 22b8dc9..57cf904 100644
--- a/doc/EFFECT_WORKFLOW.md
+++ b/doc/EFFECT_WORKFLOW.md
@@ -10,6 +10,8 @@ Automated checklist for adding new visual effects to the demo.
 
 **For ShaderToy conversions:** Use `tools/shadertoy/convert_shadertoy.py` then follow steps 3-8 below.
 
+**For SDF/raymarching effects:** See `doc/SDF_EFFECT_GUIDE.md` for streamlined workflow using SDFEffect base class.
+
 **For custom effects:** Follow all steps 1-8.
 
 ---
@@ -18,6 +20,8 @@ Automated checklist for adding new visual effects to the demo.
 
 ### 1. Create Effect Files
 
+**Description:** Each visual effect must have its own dedicated header (`.h`) and implementation (`.cc`) file pair.
+
 **Location:**
 - Header: `src/effects/<effect_name>_effect.h`
 - Implementation: `src/effects/<effect_name>_effect.cc`
@@ -84,7 +88,7 @@ SHADER_TUNNEL, NONE, shaders/tunnel.wgsl, "Tunnel effect shader"
 
 # In normal section (line ~183):
         src/effects/solarize_effect.cc
-        src/effects/tunnel_effect.cc        # <-- Add here
+        src/effects/tunnel.cc        # <-- Add here
         src/effects/chroma_aberration_effect.cc
 ```
 
@@ -92,7 +96,7 @@ SHADER_TUNNEL, NONE, shaders/tunnel.wgsl, "Tunnel effect shader"
 
 **File:** `src/gpu/demo_effects.h`
 
-**Action:** Add include directive:
+**Action:** `src/gpu/demo_effects.h` now acts as a central include file. Add a single include directive for your new effect's header:
 ```cpp
 #include "effects/<effect_name>_effect.h"
 ```