fix timezone handling and logging fallback robustness

src/vlm/reports.py

@@ -19,6 +19,13 @@ from vlm.models import SeasonCompleteness, DuplicateGroup, VideoFile, MovieIdent
 logger = logging.getLogger(__name__)
 
 
+def _normalize_to_utc(timestamp: datetime) -> datetime:
+    """Normalize a datetime to a UTC instant."""
+    if timestamp.tzinfo is None:
+        timestamp = timestamp.astimezone()
+    return timestamp.astimezone(timezone.utc)
+
+
 def generate_inventory_report(
     files: list[VideoFile],
     format: str,
@@ -87,11 +94,7 @@ def _generate_inventory_csv(
     # Write each file
     for video_file in files:
         # Format timestamp as ISO 8601 in UTC
-        if video_file.modified_timestamp.tzinfo is None:
-            # Assume local time, convert to UTC
-            modified_utc = video_file.modified_timestamp.replace(tzinfo=timezone.utc)
-        else:
-            modified_utc = video_file.modified_timestamp.astimezone(timezone.utc)
+        modified_utc = _normalize_to_utc(video_file.modified_timestamp)
         
         row = {
             'path': str(video_file.path),
@@ -127,11 +130,7 @@ def _generate_inventory_json(
     # Add each file
     for video_file in files:
         # Format timestamp as ISO 8601 in UTC
-        if video_file.modified_timestamp.tzinfo is None:
-            # Assume local time, convert to UTC
-            modified_utc = video_file.modified_timestamp.replace(tzinfo=timezone.utc)
-        else:
-            modified_utc = video_file.modified_timestamp.astimezone(timezone.utc)
+        modified_utc = _normalize_to_utc(video_file.modified_timestamp)
         
         file_data = {
             'path': str(video_file.path),