Audit per-agent memory-dir resident cost (~15k/agent on coder-venus-cc)

coder-venus-cc /context 2026-09-28: own memory dir is 15k of 191.2k resident (6.0%), always loaded. Same class of issue as the evolutiva commons-prune (see project_evolutiva_commons_prune_measurement.md) but per-agent MEMORY.md/memory-dir content instead of shared commons files - needs a per-agent prune pass across the fleet, not just Evolutiva. Route to each project's own lane once scoped.