overview: show when each vault was last updated, and by whom

Was silently dropping updatedAt/updatedBy even though the server
already returned them — the CLI just never printed them. Also
resolves updatedBy to the recipient's label server-side (matching how
grants already show a label alongside the recipient id) instead of
printing a bare recipient_id.

Verified against a live server: overview now prints "demo/production
(updated <iso timestamp> by test-box)" instead of omitting that line
entirely.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/server/adminRoutes.ts

@@ -57,6 +57,7 @@ router.get('/overview', (_req, res) => {
     vaultKey: v.vault_key,
     updatedAt: v.updated_at,
     updatedBy: v.updated_by,
+    updatedByLabel: byId.get(v.updated_by)?.label ?? null,
     grants: listGrantsForVault(v.vault_key).map(g => ({
       recipientId: g.recipient_id,
       label: byId.get(g.recipient_id)?.label ?? null,