fix(ui-tars): add HTTP status check in fetchPresetFromUrl and handle unknown operator type

1. fetchPresetFromUrl: check response.ok before parsing body. Without
   this, a 4xx/5xx response causes the YAML parser to choke on an error
   HTML page, producing a confusing error instead of a clear HTTP status.

2. runAgent switch: throw on unknown operator type instead of silently
   falling through. The operator variable is used with a non-null
   assertion (operator!) at line 202, so an unmatched case causes a
   runtime TypeError.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Ricardo-M-L

apps/ui-tars/src/main/services/runAgent.ts

@@ -161,7 +161,7 @@ export const runAgent = async (
       operatorType = 'browser';
       break;
     default:
-      break;
+      throw new Error(`Unsupported operator type: ${settings.operator}`);
   }
 
   let modelVersion = getModelVersion(settings.vlmProvider);

apps/ui-tars/src/main/store/setting.ts

@@ -132,6 +132,9 @@ export class SettingStore {
   public static async fetchPresetFromUrl(url: string): Promise<LocalStore> {
     try {
       const response = await fetch(url);
+      if (!response.ok) {
+        throw new Error(`HTTP ${response.status}: ${response.statusText}`);
+      }
       const yamlContent = await response.text();
       return await this.importPresetFromText(yamlContent);
     } catch (error) {