Fix datetime UTC import for Python 3.10 compatibility

app.py

@@ -4,7 +4,7 @@ import json
 import time
 import uuid
 import traceback
-from datetime import datetime, UTC
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import List, Dict, Any, Tuple
 
@@ -232,7 +232,7 @@ def extract_tables(file_obj) -> Tuple[str, List[str], List[str], str]:
         # Still write empty outputs & metrics so downstream code doesn’t break
         json_obj = {
             "file": original_name,
-            "extracted_at": datetime.now(UTC).isoformat().replace("+00:00", "Z"),
+            "extracted_at": datetime.now(timezone.utc).isoformat().replace("+00:00", "Z"),
             "n_pages": n_pages,
             "tables": [],
         }
@@ -259,7 +259,7 @@ def extract_tables(file_obj) -> Tuple[str, List[str], List[str], str]:
     # Write JSON + metrics
     json_obj = {
         "file": original_name,
-        "extracted_at": datetime.now(UTC).isoformat().replace("+00:00", "Z"),
+        "extracted_at": datetime.now(timezone.utc).isoformat().replace("+00:00", "Z"),
         "n_pages": n_pages,
         "tables": all_tables_json,
     }