Add a new field to the alert schema to fix a mismatch between the prior schema and the upstream NWS API

internal/normalizers/nws/alerts.go

@@ -93,12 +93,8 @@ func buildAlerts(parsed nwsAlertsResponse, fallbackAsOf time.Time) (model.Weathe
 		sent := nwscommon.ParseTimePtr(p.Sent)
 		effective := nwscommon.ParseTimePtr(p.Effective)
 		onset := nwscommon.ParseTimePtr(p.Onset)
-
-		// Expires: prefer "expires"; fall back to "ends" if present.
+		ends := nwscommon.ParseTimePtr(p.Ends)
 		expires := nwscommon.ParseTimePtr(p.Expires)
-		if expires == nil {
-			expires = nwscommon.ParseTimePtr(p.Ends)
-		}
 
 		refs := parseNWSAlertReferences(p.References)
 
@@ -123,6 +119,7 @@ func buildAlerts(parsed nwsAlertsResponse, fallbackAsOf time.Time) (model.Weathe
 			Sent:      sent,
 			Effective: effective,
 			Onset:     onset,
+			Ends:      ends,
 			Expires:   expires,
 
 			AreaDescription: strings.TrimSpace(p.AreaDesc),