F-201 F-202 F-203: POS cash close report + email + PIN admin

F-201: GET /pos/reports/cash-close/:id with financial summary, sales
  by state, payments breakdown, items sold. Extended /pos/sessions/:id.

F-202: Cash close email sent on session close to smtpReportEmail
  (best-effort). smtpReportEmail field added to admin SMTP settings.

F-203: Admin POS terminal config: selfpayMode, closeSessionRequiresPin,
  closeSessionPin (4-6 digits) with dedicated settings section.

project/frontend/src/components/checkout/CheckoutClient.tsx

@@ -45,8 +45,8 @@ function addressToForm(addr: SavedAddress) {
     phone: '',
     address: addr.street,
     city: addr.city,
-    postalCode: addr.postalCode,
-    country: addr.country,
+    postalCode: addr.postalCode ?? '',
+    country: addr.country ?? '',
   };
 }