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, 24 insertions, 0 deletions

diff --git a/src/shaders/lighting.wgsl b/src/shaders/lighting.wgsl
new file mode 100644
index 0000000..fd92c1a
--- /dev/null
+++ b/src/shaders/lighting.wgsl
@@ -0,0 +1,24 @@
+fn get_normal_basic(p: vec3f, obj_params: vec4f) -> vec3f {
+    let obj_type = obj_params.x;
+    if (obj_type == 1.0) { return normalize(p); }
+    let e = vec2f(0.001, 0.0);
+    return normalize(vec3f(
+        get_dist(p + e.xyy, obj_params) - get_dist(p - e.xyy, obj_params),
+        get_dist(p + e.yxy, obj_params) - get_dist(p - e.yxy, obj_params),
+        get_dist(p + e.yyx, obj_params) - get_dist(p - e.yyx, obj_params)
+    ));
+}
+
+fn calc_shadow(ro: vec3f, rd: vec3f, tmin: f32, tmax: f32, skip_idx: u32) -> f32 {
+    var res = 1.0;
+    var t = tmin;
+    if (t < 0.05) { t = 0.05; } 
+    for (var i = 0; i < 32; i = i + 1) {
+        let h = map_scene(ro + rd * t, skip_idx);
+        if (h < 0.001) { return 0.0; }
+        res = min(res, 16.0 * h / t); 
+        t = t + clamp(h, 0.02, 0.4);
+        if (t > tmax) { break; }
+    }
+    return clamp(res, 0.0, 1.0);
+}