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, 33 insertions, 0 deletions

diff --git a/src/shaders/heptagon.wgsl b/src/shaders/heptagon.wgsl
new file mode 100644
index 0000000..a8a450f
--- /dev/null
+++ b/src/shaders/heptagon.wgsl
@@ -0,0 +1,33 @@
+// Heptagon shader for Sequence v2
+#include "sequence_uniforms"
+#include "render/fullscreen_uv_vs"  // <- VertexOutput + vs_main
+
+// Standard v2 post-process layout (bindings 0,1 unused for scene effects)
+@group(0) @binding(2) var<uniform> uniforms: UniformsSequenceParams;
+
+fn sdf_heptagon(p: vec2f, r: f32) -> f32 {
+    let an = 3.141593 / 7.0;  // PI/7 for heptagon
+    let acs = vec2f(cos(an), sin(an));
+    let bn = (atan2(p.x, p.y) % (2.0 * an)) - an;
+    let q = length(p) * vec2f(cos(bn), abs(sin(bn)));
+    return length(q - r * acs) * sign(q.x - r * acs.x);
+}
+
+@fragment fn fs_main(in: VertexOutput) -> @location(0) vec4f {
+    let aspect = uniforms.aspect_ratio;
+    let uv = (in.uv * 2.0 - 1.0) * vec2f(aspect, 1.0);
+
+    let rotation = uniforms.beat_time * 0.5;
+    let c = cos(rotation);
+    let s = sin(rotation);
+    let rot_uv = vec2f(
+        uv.x * c - uv.y * s,
+        uv.x * s + uv.y * c
+    );
+
+    let dist = sdf_heptagon(rot_uv, 0.3);
+    let color = mix(vec3f(0.2, 0.4, 0.8), vec3f(1.0, 0.8, 0.2),
+                    smoothstep(0.01, -0.01, dist));
+
+    return vec4f(color, 1.0);
+}