fix(cnn_v3): shadow pass — 5 bugs fixed, labels in gbuf_view

1. Camera Y-inversion: proj.m[5] = -proj.m[5] in upload_scene_data
   + WGPUFrontFace_CCW on raster pipeline.
2. Shadow formula: replace shadowWithStoredDistance with 64-step
   IQ soft shadow (8*d/t, unbounded).
3. Local→world SDF scale: d *= length(obj.model[0].xyz).
4. Shadow bias: use rasterized normal from normal_mat_tex (binding 4)
   instead of light direction — fixes terminator self-shadow on spheres.
5. ShaderComposer: GBufViewEffect now resolves #include via
   ShaderComposer::Get().Compose().

Also: per-tile channel labels in gbuf_view.wgsl via debug_str.
Scene simplified to 1 cube + 1 sphere for debugging (restore TODO).
Scale propagation for pulsating sphere confirmed correct end-to-end.

handoff(Gemini): shadow validated. Next: restore full scene in
GBufferEffect::set_scene() (20 cubes + 4 spheres, 2 lights), then
run training pass per cnn_v3/docs/HOWTO.md §3.

1 files changed, 3 insertions, 1 deletions

diff --git a/cnn_v3/src/gbuf_view_effect.cc b/cnn_v3/src/gbuf_view_effect.cc
index 180919d..ccf80b0 100644
--- a/cnn_v3/src/gbuf_view_effect.cc
+++ b/cnn_v3/src/gbuf_view_effect.cc
@@ -10,6 +10,7 @@
 #endif
 
 #include "gpu/gpu.h"
+#include "gpu/shader_composer.h"
 #include "util/asset_manager.h"
 #include "util/fatal_error.h"
 
@@ -63,7 +64,8 @@ GBufViewEffect::GBufViewEffect(const GpuContext& ctx,
   // Shader module
   WGPUShaderSourceWGSL wgsl_src = {};
   wgsl_src.chain.sType = WGPUSType_ShaderSourceWGSL;
-  wgsl_src.code        = str_view(gbuf_view_wgsl);
+  const std::string composed = ShaderComposer::Get().Compose({}, gbuf_view_wgsl);
+  wgsl_src.code        = str_view(composed.c_str());
   WGPUShaderModuleDescriptor shader_desc = {};
   shader_desc.nextInChain = &wgsl_src.chain;
   WGPUShaderModule shader =