🚑 fix: safeguard NewAPIError.Error() against nil pointer panic

Backend
• `types/error.go`
  – Return empty string when receiver itself is `nil`.
  – If `Err` is `nil`, fall back to `errorCode` string to avoid calling `nil.Error()`.

This prevents runtime panics when the error handler builds an OpenAI-style error response but the underlying `Err` field has not been set.

web/src/components/table/LogsTable.js

@@ -410,7 +410,7 @@ const LogsTable = () => {
         return isAdminUser ? (
           <div>
             <Avatar
-              size='small'
+              size='extra-small'
               color={stringToColor(text)}
               style={{ marginRight: 4 }}
               onClick={(event) => {