`container_run` logs every stdout line at INFO (target `nixos-container`)
as operation progress. For the read-only `list` op — called on the hot
path (dashboard rescan, forge + boot sweeps) — that stdout is the return
value, not progress, so every call logs the full ~28-line container roster
at INFO. hive-c0re calls it several times a second, flooding the host
journal.
Gate the stdout per-line INFO logging on the op not being `list`. Mutating
ops still log their progress; stderr is still logged for every op (errors
matter regardless). No behaviour change beyond log volume.
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