feat: enhance receipt import to support PDF files with updated UI and backend processing

backend/src/receipt-import/receipt-import.controller.ts

@@ -16,6 +16,7 @@ const ALLOWED_MIMES = [
   'image/webp',
   'image/heic',
   'image/heif',
+  'application/pdf',
 ];
 
 @Controller('receipt-import')
@@ -37,7 +38,7 @@ export class ReceiptImportController {
     }
     if (!ALLOWED_MIMES.includes(file.mimetype)) {
       throw new BadRequestException(
-        'Otillåten filtyp. Använd JPEG, PNG eller WebP.',
+        'Otillåten filtyp. Använd JPEG, PNG, WebP eller PDF.',
       );
     }
     return this.receiptImportService.parseReceipt(file);