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, 30 insertions, 0 deletions

diff --git a/src/shaders/math/sdf_shapes.wgsl b/src/shaders/math/sdf_shapes.wgsl
new file mode 100644
index 0000000..2dfae3e
--- /dev/null
+++ b/src/shaders/math/sdf_shapes.wgsl
@@ -0,0 +1,30 @@
+// 3D SDF primitives
+fn sdSphere(p: vec3f, r: f32) -> f32 {
+    return length(p) - r;
+}
+
+fn sdBox(p: vec3f, b: vec3f) -> f32 {
+    let q = abs(p) - b;
+    return length(max(q, vec3f(0.0))) + min(max(q.x, max(q.y, q.z)), 0.0);
+}
+
+fn sdTorus(p: vec3f, t: vec2f) -> f32 {
+    let q = vec2f(length(p.xz) - t.x, p.y);
+    return length(q) - t.y;
+}
+
+fn sdPlane(p: vec3f, n: vec3f, h: f32) -> f32 {
+    return dot(p, n) + h;
+}
+
+// 2D SDF primitives
+fn sdBox2D(p: vec2f, b: vec2f) -> f32 {
+    let d = abs(p) - b;
+    return length(max(d, vec2f(0.0))) + min(max(d.x, d.y), 0.0);
+}
+
+// Approximate
+fn sdEllipse(p: vec2f, ab: vec2f) -> f32 {
+    let d = length(p / ab);
+    return length(p) * (1.0 - 1.0 / d);
+}