* feat(perf): cover pipeline throughput (cpm) in performance probe
Mirror the analysis pipeline's tpm for covers. A new coverPerfStore samples the
backfill `done` progress from cover:library-progress events and derives a rolling
one-minute covers-per-minute rate. Surfaced as a live diag in perfLiveStore, a
pinnable "Cover backfill" throughput card in the Monitor tab, and a cpm row in
the Cover pipeline overlay block.
* docs(changelog): note cover pipeline cpm metric (PR #945)
Add CHANGELOG entry and credits line for the cover-pipeline covers-per-minute
throughput metric in the Performance Probe.
cucadmuh