feat: track upstream request ID and prevent response header override

When proxying through another new-api instance, the upstream
X-Oneapi-Request-Id was overwriting the local one in client responses.
This adds a new `upstream_request_id` field to the logs table, captures
the upstream ID during relay, and filters it from being copied back to
the client. Frontend gains search/filter and detail display support.

web/default/src/features/usage-logs/components/dialogs/details-dialog.tsx

@@ -519,6 +519,13 @@ export function DetailsDialog(props: DetailsDialogProps) {
                   mono
                 />
               )}
+              {props.log.upstream_request_id && (
+                <DetailRow
+                  label={t('Upstream Request ID')}
+                  value={props.log.upstream_request_id}
+                  mono
+                />
+              )}
 
               {props.isAdmin && props.log.channel > 0 && (
                 <DetailRow