refactor(gpu): Implement compile-time BVH toggle via shader composition

Completed Task #18-B optimization and refactoring.
- Replaced runtime branching in shader with compile-time snippet substitution in ShaderComposer.
- Added 'scene_query_bvh.wgsl' and 'scene_query_linear.wgsl' as distinct snippets.
- Refactored Renderer3D to manage two separate pipelines (with and without BVH).
- Updated ShaderComposer to support snippet substitution during composition.
- Verified both paths with test_3d_render (default and --no-bvh).
- Removed temporary shader hacks and cleaned up renderer_3d.wgsl.

1 files changed, 2 insertions, 1 deletions

diff --git a/assets/final/demo_assets.txt b/assets/final/demo_assets.txt
index 5ba2ec2..c38da51 100644
--- a/assets/final/demo_assets.txt
+++ b/assets/final/demo_assets.txt
@@ -44,5 +44,6 @@ SHADER_SKYBOX, NONE, shaders/skybox.wgsl, "Skybox background shader"
 SHADER_MATH_SDF_SHAPES, NONE, shaders/math/sdf_shapes.wgsl, "SDF Shapes Snippet"
 SHADER_MATH_SDF_UTILS, NONE, shaders/math/sdf_utils.wgsl, "SDF Utils Snippet"
 SHADER_RENDER_SHADOWS, NONE, shaders/render/shadows.wgsl, "Shadows Snippet"
-SHADER_RENDER_SCENE_QUERY, NONE, shaders/render/scene_query.wgsl, "Scene Query Snippet"
+SHADER_RENDER_SCENE_QUERY_BVH, NONE, shaders/render/scene_query_bvh.wgsl, "Scene Query Snippet (BVH)"
+SHADER_RENDER_SCENE_QUERY_LINEAR, NONE, shaders/render/scene_query_linear.wgsl, "Scene Query Snippet (Linear)"
 SHADER_RENDER_LIGHTING_UTILS, NONE, shaders/render/lighting_utils.wgsl, "Lighting Utils Snippet"
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