/scenarios — table of all scenarios with filter chips (all/cartesian/
user). Cartesian scenarios get a neutral badge; user-defined get an
emerald accent. Empty-state nudges the user to run /recompute.
/scenarios/:id — params summary + the latest persisted MC projection.
Reuses FanChart so chart code is shared with /what-if. 404 on the
projection endpoint is treated as "no run yet" (don't retry); other
errors surface normally.
Nav grew a Scenarios tab. typecheck + 5 tests + build pass.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
