Move the 6 parametrized workflow scenarios from scenario/workflows.rs
into a new workflow/ directory with one file per test. Move fixture
.fabro files from test/scenario/ to workflow/fixtures/ co-located with
the tests.
Rename the scenario_tests! macro to sandbox_tests! in the new module
for clarity. Slim scenario/ down to just lifecycle and exec tests.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
