chore(studio): remove unused isMissingFileError

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/studio/src/api/errors.ts

@@ -15,6 +15,3 @@ export class ApiError extends Error {
   }
 }
 
-export function isMissingFileError(error: unknown): boolean {
-  return (error as NodeJS.ErrnoException | undefined)?.code === "ENOENT";
-}