fix(auxiliary): custom provider URL rewrite + main_runtime model for title gen

- auxiliary_client: apply _to_openai_base_url() to custom base_url
  (fixes /anthropic → /v1 rewrite missing for provider="custom")
- auxiliary_client: use main_runtime.get("model") instead of _read_main_model()
  so auxiliary tasks follow system default model changes
- title_generator: thread main_runtime through generate_title → auto_title_session → maybe_auto_title
- cli.py / gateway/run.py: pass main_runtime to maybe_auto_title
- tests: update mock assertions for new main_runtime parameter

gateway/run.py

@@ -10700,6 +10700,13 @@ class GatewayRunner:
                         final_response,
                         all_msgs,
                         failure_callback=_title_failure_cb,
+                        main_runtime={
+                            "model": getattr(agent, "model", None),
+                            "provider": getattr(agent, "provider", None),
+                            "base_url": getattr(agent, "base_url", None),
+                            "api_key": getattr(agent, "api_key", None),
+                            "api_mode": getattr(agent, "api_mode", None),
+                        } if agent else None,
                     )
                 except Exception:
                     pass