fix(spaces): module-level @spaces.GPU so ZeroGPU's startup detector finds it

fix(spaces): use \$HOME instead of /data (no persistent-storage add-on needed)

feat: API-format workflows + sidebar nav + responsive UI

fix(backend): pass cache_args to PromptExecutor + dump worker tracebacks

fix(backend,models): runtime corrections from end-to-end testing

ci: run unit tests + ruff lint on every push

feat(backend): submit() async generator with progress hooks + ZeroGPU

feat(backend): ComfyUILibraryBackend skeleton + event dataclasses