feat: transaction activity audit and account activity audit

internal/model/account_activity.go

@@ -0,0 +1,18 @@
+package model
+
+import "time"
+
+// AccountActivityRow is a unified row representing either an account-scoped space
+// audit entry or a transaction audit entry that belongs to the account. Exactly one
+// of SpaceLog / TxLog is set.
+type AccountActivityRow struct {
+	SpaceLog *SpaceAuditLogWithActor
+	TxLog    *TransactionAuditLogWithActor
+}
+
+func (r AccountActivityRow) Timestamp() time.Time {
+	if r.SpaceLog != nil {
+		return r.SpaceLog.CreatedAt
+	}
+	return r.TxLog.CreatedAt
+}