Simplify error handling in processEmailJob

Remove unnecessary instanceof check since String() handles all types consistently.

src/jobs/processEmailJob.ts

@@ -64,7 +64,7 @@ export const processEmailJob = {
         }
       }
     } catch (error) {
-      throw new Error(`Failed to process email ${emailId}: ${error instanceof Error ? error.message : String(error)}`)
+      throw new Error(`Failed to process email ${emailId}: ${String(error)}`)
     }
   }
 }