feat: reminder due calculation

app/api/vouchers/route.ts

@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { getDb } from "@/lib/db";
 import { getVoucherStatus } from "@/lib/voucher-status";
 import { validateVoucher, isExpiringSoon } from "@/lib/vouchers";
+import { parseReminderDays } from "@/lib/reminders";
 
 export async function GET(req: NextRequest) {
   const filter = req.nextUrl.searchParams.get("filter");
@@ -47,6 +48,11 @@ export async function POST(req: NextRequest) {
       kategorie: input.kategorie,
       notiz: input.notiz,
       contacts: contactIds.length ? { create: contactIds.map((contactId) => ({ contactId })) } : undefined,
+      rules: {
+        create: parseReminderDays(
+          typeof body.reminderDays === "string" ? body.reminderDays : Array.isArray(body.reminderDays) ? body.reminderDays.join(",") : undefined
+        ).map((tageVorher) => ({ tageVorher })),
+      },
     },
   });
   return NextResponse.json(created, { status: 201 });