fix(agent): report THREAD_REPAIRED as lifecycle error code

The send-path repair branch set _request_result but not
_request_error_code, so the AGENT_REQUEST_FAILED lifecycle event fell back
to the misleading 'agent lifecycle failure'. Set THREAD_REPAIRED so logs
and middleware show the real outcome.

agent/src/ss_tools/agent/app.py

@@ -1081,6 +1081,7 @@ async def agent_handler(  # noqa: C901 — intentionally complex C4 orchestratio
                             extra={"src": "AgentChat.GradioApp.Handler"},
                         )
                         _request_result = "failed"
+                        _request_error_code = "THREAD_REPAIRED"
                         yield json.dumps(
                             {
                                 "content": "⚠️ Предыдущий запуск был прерван. Поток восстановлен — отправьте запрос ещё раз.",