Propagate resolved proxy policy through auth routing (#34649)

## Why

Auth routing represented the default proxy policy as an absent configuration,
leaving consumers to reconstruct the fallback HTTP client independently. Carry
the application's resolved policy explicitly so auth and related requests use
the same client configuration.

## What changed

- Build `AuthRouteConfig` from the resolved `HttpClientFactory` for both
  `ReqwestDefault` and `RespectSystemProxy` policies.
- Pass that route configuration through login, auth, cloud task, and cloud
  configuration flows, and reuse its factory when loading cloud configuration.
- Log cloud-task configuration load failures before falling back to the
  transport-default proxy policy.

## Testing

Extended configuration tests to verify that effective and bootstrap auth routes
select the expected proxy policy when system-proxy support is enabled or
disabled by feature requirements.

GitOrigin-RevId: d03802e2660f5cf6d940e8e718ec5c82ede7eab1

codex-rs/exec/src/lib.rs

@@ -491,7 +491,7 @@ pub async fn run_main(cli: Cli, arg0_paths: Arg0DispatchPaths) -> anyhow::Result
         forced_login_method: config.forced_login_method,
         forced_chatgpt_workspace_id: config.forced_chatgpt_workspace_id.clone(),
         chatgpt_base_url: Some(config.chatgpt_base_url.clone()),
-        auth_route_config,
+        auth_route_config: Some(auth_route_config),
     })
     .await
     {