Improve error reporting

Log an error when images/dates do not match. Also, show the response
body in the error modal on the client side.

index.html

@@ -102,10 +102,12 @@
                         "Successfully uploaded receipts"
                     );
                 } else {
+                    r.text().then((msg) => {
                         showDialog(
                             "Upload Failure",
-                        `Failed to upload receipts: ${r.statusText}`,
+                            `Failed to upload receipts: ${r.statusText}\n${msg}`,
                         );
+                    });
                 }
                 form.reset();
             })

receipts.py

@@ -92,10 +92,14 @@ async def upload_receipts(
     #    notes: Annotated[list[str], fastapi.Form(alias='notes[]')],
 ):
     if len(dates) != len(images):
+        msg = (
+            f'Number of uploaded images ({len(images)})'
+            f' does not match number of date fields ({len(dates)})'
+        )
+        log.warning('%s', msg)
         raise fastapi.HTTPException(
             status_code=fastapi.status.HTTP_400_BAD_REQUEST,
-            detail='Number of uploaded images does not match '
-            'number of date fields',
+            detail=msg,
         )
     failed = False
     async with Paperless() as paperless: