fix(stream-check): add missing error_category field in fallback

The error_category field was added to StreamCheckResult in this branch
but the fallback constructor in stream_check_all_providers was not
updated, which broke cargo build.

src-tauri/src/commands/stream_check.rs

@@ -133,6 +133,7 @@ pub async fn stream_check_all_providers(
                 model_used: String::new(),
                 tested_at: chrono::Utc::now().timestamp(),
                 retry_count: 0,
+                error_category: None,
             }
         });