New [user.retention] TOML sub-block with auto_close_days and
auto_delete_days. Both default to 0, which disables the respective
sweep — a conservative default that preserves current behaviour for
existing deployments and lets admins test auto-close in isolation.
Only parsing + the test User literals are touched here; the actual
lazy sweep consuming these values lands in the next commit.
Brummel
e5a62d8f10