Memory version history and Restore

The Memory detail page now surfaces a Version history section. Every edit already snapshots the prior text into a version ledger; that history is now visible as a newest-first timeline — the current version is marked, and each past version shows its version number, when it was saved, and a snippet of its text. Owners can restore any past version with one click (behind an inline "Restore to v{n}?" confirm). Restoring archives your current text into history first, so nothing is lost, then re-applies and re-embeds the chosen version so search stays accurate. When there are no edits yet, the section explains that history starts after the first change.