feat: Implement workspace system (Task #77)

Self-contained workspaces for parallel demo development.

Structure:
- workspaces/main,test - Demo-specific resources
- assets/common - Shared resources
- workspace.cfg - Configuration per workspace

CMake integration:
- DEMO_WORKSPACE option (defaults to main)
- cmake/ParseWorkspace.cmake - Config parser
- Workspace-relative asset/timeline/music paths

Migration:
- Main demo: demo.seq to workspaces/main/timeline.seq
- Test demo: test_demo.seq to workspaces/test/timeline.seq
- Common shaders: assets/common/shaders
- Workspace shaders: workspaces/*/shaders

Build:
cmake -B build -DDEMO_WORKSPACE=main
cmake -B build_test -DDEMO_WORKSPACE=test

All tests passing (36/36).

handoff(Claude): Task #77 workspace system complete. Both main and test workspaces build and pass all tests.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/workspaces/test/shaders/compute/gen_grid.wgsl b/workspaces/test/shaders/compute/gen_grid.wgsl
new file mode 100644
index 0000000..cc5e189
--- /dev/null
+++ b/workspaces/test/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));
+}