Task 458: Add Mass Boundary and Fleet Intercept Charts to EP04

Status: DONE

Summary

EP04 already has 4 timeseries charts + 1 bar chart + 1 margin gauge, but two key analyses lack visualization:

1. Mass boundary chart: The 65%-thrust mass-vs-transit analysis (exploration-01) shows 48,000t→105 days vs 300t→8.3 days. A chart makes the mass mystery visually stark — this is central to the project's core finding.
2. Fleet intercept timeline chart: The 33-hour deadline (transfer-05) breaks down into 9.7h transit + 23.3h repair + arrival. No chart shows this breakdown — the headline "33 hours" understates the urgency.

Plan

1. Add mass boundary timeseries chart after exploration-01 (mass vs transit time)
2. Add fleet timeline bar chart showing time budget breakdown
3. Add content validation tests
4. Run all tests, commit, push