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/compute/gen_grid.wgsl b/src/shaders/compute/gen_grid.wgsl
new file mode 100644
index 0000000..4ce7ea3
--- /dev/null
+++ b/src/shaders/compute/gen_grid.wgsl
@@ -0,0 +1,24 @@
+// GPU procedural grid pattern generator.
+// Simple grid lines with configurable spacing and thickness.
+
+struct GridParams {
+  width: u32,
+  height: u32,
+  grid_size: u32,
+  thickness: u32,
+}
+
+@group(0) @binding(0) var output_tex: texture_storage_2d<rgba8unorm, write>;
+@group(0) @binding(1) var<uniform> params: GridParams;
+
+@compute @workgroup_size(8, 8, 1)
+fn main(@builtin(global_invocation_id) id: vec3<u32>) {
+  if (id.x >= params.width || id.y >= params.height) { return; }
+
+  let on_line = (id.x % params.grid_size) < params.thickness ||
+                (id.y % params.grid_size) < params.thickness;
+
+  let val = select(0.0, 1.0, on_line);
+
+  textureStore(output_tex, id.xy, vec4f(val, val, val, 1.0));
+}