'Validation Throughput (tests/week)' was time-dependent — director wanted
an activity-based metric instead.
New metric: Pipeline Conversion Rate
formula: validated / (validated + rejected + in_review) × 100
unit: % (no time reference)
meaning: 'of all tests that have entered validation, X% succeeded'
trend: declining if in_review backlog > validated count,
improving if conversion ≥ 80%, stable otherwise
Backend: calculate_validation_throughput() rewritten — same API key
(tests_per_week) kept for compatibility, new conversion_rate field added.
Frontend: label → 'Pipeline Conversion', unit → '%', tooltip updated.
