Fix client-side cache staleness after proof of payment upload

Added cache revalidation to ensure ViewLocationCard reflects uploaded
proof of payment when navigating back from ViewBillCard:

- Server-side: Added revalidatePath() to upload actions in billActions
  and locationActions to invalidate Next.js server cache
- Client-side: Added router.refresh() calls in ViewBillCard and
  ViewLocationCard to refresh client router cache after successful upload

This maintains the current UX (no redirect on upload) while ensuring
fresh data is displayed on navigation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/ui/ViewLocationCard.tsx

@@ -5,6 +5,7 @@ import { BilledTo, BillingLocation, UserSettings } from "../lib/db-types";
 import { formatYearMonth } from "../lib/format";
 import { formatCurrency, formatIban } from "../lib/formatStrings";
 import { useTranslations } from "next-intl";
+import { useRouter } from "next/navigation";
 import { ViewBillBadge } from "./ViewBillBadge";
 import { Pdf417Barcode } from "./Pdf417Barcode";
 import { EncodePayment, PaymentParams } from "hub-3a-payment-encoder";
@@ -34,6 +35,7 @@ export const ViewLocationCard: FC<ViewLocationCardProps> = ({ location, userSett
         proofOfPaymentType,
     } = location;
 
+    const router = useRouter();
     const t = useTranslations("home-page.location-card");
 
     const [isUploading, setIsUploading] = useState(false);
@@ -64,6 +66,7 @@ export const ViewLocationCard: FC<ViewLocationCardProps> = ({ location, userSett
             if (result.success) {
                 setAttachmentFilename(file.name);
                 setAttachmentUploadedAt(new Date());
+                router.refresh();
             } else {
                 setUploadError(result.error || 'Upload failed');
             }