mix continuum.archive_continued_chains (continuum v0.5.0)

Deletes expired non-tail runs from continue_as_new chains.

mix continuum.archive_continued_chains --repo MyApp.Repo --older-than 30d
mix continuum.archive_continued_chains --repo MyApp.Repo --older-than 30d --execute

The task is a dry run by default. v0.4 performs deletion, not archival into a separate table. A run is eligible only when it is a completed non-tail cycle, older than the cutoff, past retention_until, and not part of a child chain whose parent is still non-terminal.