Remediation: Implement shared common/shaders/ directory

Eliminates 36 duplicate shader files across workspaces.

Structure:
- common/shaders/{math,render,compute}/ - Shared utilities (20 files)
- workspaces/*/shaders/ - Workspace-specific only

Changes:
- Created common/shaders/ with math, render, compute subdirectories
- Moved 20 common shaders from workspaces to common/
- Removed duplicates from test workspace
- Updated assets.txt: ../../common/shaders/ references
- Enhanced asset_packer.cc: filesystem path normalization for ../ resolution

Implementation: Option 1 from SHADER_REUSE_INVESTIGATION.md
- Single source of truth for common code
- Workspace references via relative paths
- Path normalization in asset packer

handoff(Claude): Common shader directory implemented

1 files changed, 24 insertions, 0 deletions

diff --git a/common/shaders/compute/gen_grid.wgsl b/common/shaders/compute/gen_grid.wgsl
new file mode 100644
index 0000000..cc5e189
--- /dev/null
+++ b/common/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, vec4<f32>(val, val, val, 1.0));
+}