U04 — Coverage health narrative

Backlog: FIS-UX-004, FIS-UX-010, FIS-UX-021

Plan

Coverage leads with a health verdict and outcome language; snake_case keys remain in Advanced.

Do

1. Health summary strip when metrics are zero (“Platform coverage healthy”).
2. Human metric names + why-zero-is-good explanations.
3. Show generated_at provenance footer from API.

Check

scripts/fi-studio-ux-pdca/check-phase-gate.sh U04

Act

Refine coverage narrative and provenance until U04 gate is green; then proceed to U05.