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, 16 insertions, 0 deletions

diff --git a/workspaces/test/shaders/ray_box.wgsl b/workspaces/test/shaders/ray_box.wgsl
new file mode 100644
index 0000000..d56ea1b
--- /dev/null
+++ b/workspaces/test/shaders/ray_box.wgsl
@@ -0,0 +1,16 @@
+struct RayBounds {
+    t_entry: f32,
+    t_exit: f32,
+    hit: bool,
+};
+
+fn ray_box_intersection(ro: vec3<f32>, rd: vec3<f32>, extent: vec3<f32>) -> RayBounds {
+    let inv_rd = 1.0 / rd;
+    let t0 = (-extent - ro) * inv_rd;
+    let t1 = (extent - ro) * inv_rd;
+    let tmin_vec = min(t0, t1);
+    let tmax_vec = max(t0, t1);
+    let t_entry = max(0.0, max(tmin_vec.x, max(tmin_vec.y, tmin_vec.z)));
+    let t_exit = min(tmax_vec.x, min(tmax_vec.y, tmax_vec.z));
+    return RayBounds(t_entry, t_exit, t_entry <= t_exit);
+}