improved robustness of time serialization system

shared/utils/time.ts

@@ -1,5 +1,8 @@
 export function toDateTime(date: Date): string {
     console.log(date);
+    if (typeof date === 'string') {
+        date = new Date(date);
+    }
     // This produces a CST-local time because server runs in CST
     const year   = date.getFullYear();
     const month  = (date.getMonth() + 1).toString().padStart(2, "0");