refactor: move common/shaders/ to src/shaders/

Relocates shared WGSL shaders under src/ where all source code lives,
eliminating the top-level common/ directory.

- Update asset references in workspaces/main/assets.txt and workspaces/test/assets.txt
- Update docs: PROJECT_CONTEXT.md, ARCHITECTURE.md, WORKSPACE_SYSTEM.md, SHADER_REUSE_INVESTIGATION.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/shaders/render/lighting_utils.wgsl b/src/shaders/render/lighting_utils.wgsl
new file mode 100644
index 0000000..f805860
--- /dev/null
+++ b/src/shaders/render/lighting_utils.wgsl
@@ -0,0 +1,6 @@
+fn calculate_lighting(color: vec3f, normal: vec3f, pos: vec3f, shadow: f32) -> vec3f {
+    let light_dir = normalize(vec3f(1.0, 1.0, 1.0));
+    let diffuse = max(dot(normal, light_dir), 0.0);
+    let lighting = diffuse * (0.1 + 0.9 * shadow) + 0.1; // Ambient + Shadowed Diffuse
+    return color * lighting;
+}