Get the normalized call detail timeline and KPI summary

Returns a normalized "call detail" payload — a KPI summary, the DEV-213 transcription metrics (ring time, silence %, overtalk %), and a time-ordered event timeline.

The payload is generated on demand and cached per call. Generation is idempotent, so the endpoint is safe to call repeatedly. Pass refresh=true to force regeneration (e.g. after the call or its transcription has been updated).