Rename Cycle Time metric to Average Duration

The analytics metric labeled "Cycle Time" actually measures average per-run test duration, not the manufacturing inter-completion cadence the term implies. Renamed it to remove the ambiguity for test and process engineers.

• Renamed the "Cycle Time" KPI card, duration chart tooltip, and phase analysis headline to "Average Duration"
• Clarified that the value reflects average passing-run execution time, not unit-to-unit cadence