Sync → Retention sweep for trashed deletions

[revett]

• Soft deleted objects accumulate under .geode/trash/ indefinitely; nothing prunes them, so a busy vault grows the bucket without bound and keeps deleted content recoverable forever rather than for a bounded window
• The soft delete window introduced in Soft delete window for synced deletions #53 has no upper edge, a retention period would cap both storage cost and how long deleted bytes linger before they are truly gone