Refactor types to support per-bill proof of payment

- Renamed BillAttachment to FileAttachment for better generalization
- Added uploadedAt field to FileAttachment (consolidates timestamp)
- Renamed utilBillsProofOfPaymentAttachment to utilBillsProofOfPayment
- Removed separate utilBillsProofOfPaymentUploadedAt field (now in FileAttachment)
- Added rentProofOfPayment field to BillingLocation for rent-specific proof
- Added proofOfPayment field to Bill interface for per-bill attachments
- Removed unused imports (ObjectId, inter)

This refactoring enables both "combined" (location-level) and "per-bill"
proof of payment attachment strategies.

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

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

app/lib/db-types.ts

@@ -1,12 +1,11 @@
-import { ObjectId } from "mongodb";
-import { inter } from "../ui/fonts";
 
-export interface BillAttachment {
+export interface FileAttachment {
     fileName: string;
     fileSize: number;
     fileType: string;
     fileLastModified: number;
     fileContentsBase64: string;
+    uploadedAt: Date;
 };
 
 export interface YearMonth {
@@ -79,9 +78,9 @@ export interface BillingLocation {
     /** (optional) whether the location has been seen by tenant */
     seenByTenantAt?: Date | null;
     /** (optional) utility bills proof of payment attachment */
-    utilBillsProofOfPaymentAttachment?: BillAttachment|null;
-    /** (optional) date when utility bills proof of payment was uploaded */
-    utilBillsProofOfPaymentUploadedAt?: Date|null;
+    utilBillsProofOfPayment?: FileAttachment|null;
+    /** (optional) rent proof of payment attachment */
+    rentProofOfPayment?: FileAttachment|null;
 };
 
 export enum BilledTo {
@@ -101,7 +100,7 @@ export interface Bill {
     /** payed amount amount in cents */
     payedAmount?: number | null;
     /** attached document (optional) */
-    attachment?: BillAttachment|null;
+    attachment?: FileAttachment|null;
     /**
      * true if there an attachment
      * @description this field enables us to send this info to the client without sending large attachment - it's an optimization
@@ -116,4 +115,6 @@ export interface Bill {
     barcodeImage?:string;
     /** (optional) HUB-3A text for generating PDF417 bar code */
     hub3aText?:string;
+    /** (optional) proof of payment attachment */
+    proofOfPayment?: FileAttachment|null;
 };