fix: persist token usage data for non-streaming chat responses (#22166)

The non-streaming response handler was saving assistant messages without
their usage/token data. While the streaming handler correctly extracted
and saved usage information, the non-streaming path discarded it entirely.

This caused assistant messages from non-streaming completions to have
NULL usage in the chat_message table, making them invisible to the
analytics token aggregation queries and contributing to the '0 tokens'
display in Admin Panel Analytics.

Extract and normalize the usage data from the API response and include
it in the database upsert, matching the pattern already used by the
streaming handler.

backend/open_webui/utils/middleware.py

@@ -3093,6 +3093,9 @@ async def non_streaming_chat_response_handler(response, ctx):
                     )
 
                     # Save message in the database
+                    raw_usage = response_data.get("usage", {}) or {}
+                    usage = normalize_usage(raw_usage) if raw_usage else None
+
                     Chats.upsert_message_to_chat_by_id_and_message_id(
                         metadata["chat_id"],
                         metadata["message_id"],
@@ -3100,6 +3103,7 @@ async def non_streaming_chat_response_handler(response, ctx):
                             "role": "assistant",
                             "content": content,
                             "output": response_output,
+                            **({"usage": usage} if usage else {}),
                         },
                     )