Task 416: Add Calculation JSON Structural Validation Tests

Status: DONE

Summary

The 14 calculation JSON files in reports/data/calculations/ have no structural validation tests. Add tests verifying: required top-level keys exist, _meta fields are present, numeric values are finite and within plausible ranges, and per-episode calculation keys match expected schemas.

Rationale

• Calculation files drive all numerical analysis — malformed data would silently corrupt reports
• npm run recalculate can overwrite these files — no test catches schema violations
• CLAUDE.md: "Reproducible numerical analysis" requires verified outputs
• Task 412 already validates calculation→report consistency; this validates the calculations themselves