Removes terminal jobs past the retention period.

Deletes :completed, :cancelled, and :discarded jobs older than retention_period. Ticks every prune_interval ms.

start_link/1 options

• :interval — tick period in ms (default from Kathikon.Config)
• :storage — module implementing Kathikon.Backend.Storage callbacks
• :name — registered name (default Kathikon.Pruner; use false in tests)

Mnesia is coordination storage, not long-term history — export metrics via telemetry for durable audit trails.

See docs/guides/configuration.md.