Refactor: Reorganize workspaces and remove assets/ directory

Workspace structure now:
- workspaces/{main,test}/obj/      (3D models)
- workspaces/{main,test}/shaders/  (WGSL shaders)
- workspaces/{main,test}/music/    (audio samples)

Changes:
- Moved workspaces/*/assets/music/ → workspaces/*/music/
- Updated assets.txt paths (assets/music/ → music/)
- Moved test_demo.{seq,track} to tools/
- Moved assets/originals/ → tools/originals/
- Removed assets/common/ (legacy, duplicated in workspaces)
- Removed assets/final/ (legacy, superseded by workspaces)
- Updated hot-reload paths in main.cc
- Updated CMake references for test_demo and validation
- Updated gen_spectrograms.sh paths

handoff(Claude): Workspace reorganization complete

1 files changed, 0 insertions, 0 deletions

diff --git a/workspaces/main/music/KICK_606.spec b/workspaces/main/music/KICK_606.spec
new file mode 100644
index 0000000..10af84a
--- /dev/null
+++ b/workspaces/main/music/KICK_606.spec