fix(factory): render an unavailable change-failure rate instead of 0.0 percent

[castrojo]

Problem

pct(n) in MetricsPanels.tsx multiplies null by 100, so fetch-dora.js missing changeFailureRate data is shown as 0.0%.

Evidence

The expression (null * 100).toFixed(1) + "%" outputs 0.0%, even though fetch-dora.js deliberately emits null when no terminal runs exist.

Expected

Render an unavailable marker for null/non-finite inputs and reserve zero for real measured values.