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, 31 insertions, 0 deletions

diff --git a/workspaces/main/shaders/visual_debug.wgsl b/workspaces/main/shaders/visual_debug.wgsl
new file mode 100644
index 0000000..63e1f13
--- /dev/null
+++ b/workspaces/main/shaders/visual_debug.wgsl
@@ -0,0 +1,31 @@
+struct GlobalUniforms {
+    view_proj: mat4x4<f32>,
+    inv_view_proj: mat4x4<f32>,
+    camera_pos_time: vec4<f32>,
+    params: vec4<f32>,
+    resolution: vec2<f32>,
+};
+@group(0) @binding(0) var<uniform> uniforms : GlobalUniforms;
+
+struct VertexInput {
+    @location(0) position : vec3<f32>,
+    @location(1) color : vec3<f32>,
+}
+
+struct VertexOutput {
+    @builtin(position) position : vec4<f32>,
+    @location(0) color : vec3<f32>,
+}
+
+@vertex
+fn vs_main(in : VertexInput) -> VertexOutput {
+    var out : VertexOutput;
+    out.position = uniforms.view_proj * vec4<f32>(in.position, 1.0);
+    out.color = in.color;
+    return out;
+}
+
+@fragment
+fn fs_main(in : VertexOutput) -> @location(0) vec4<f32> {
+    return vec4<f32>(in.color, 1.0);
+}