Fix: memory "updated" dates and feed ordering

Memory "updated X ago" labels and All Memories feed ordering were wrong for most existing memories — showing the time of a background data migration rather than the actual last edit. The root cause was an overly broad database trigger that recorded every internal update (topic assignment, embedding refresh) as a content edit. The trigger has been tightened to only advance the timestamp when title, content, or tags actually change, and a one-time restore pulled every affected memory's timestamp back to its true edit time from append-only ledgers.