Require auth managers to receive routing configuration (#34650)

## Why

Auth managers should use the application's resolved HTTP client factory instead
of silently falling back to the transport's default proxy behavior.

## What changed

- Make `AuthRouteConfig` required when constructing an `AuthManager` or
  `AuthConfig`.
- Pass each production caller's resolved routing configuration through without
  wrapping it in an optional value.
- Add a test helper that explicitly selects the transport-default proxy policy
  for callers that do not exercise custom routing.

GitOrigin-RevId: d89a3b1f8b5d4007650cdac0aae241c94d598580

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: Some(auth_route_config),
+        auth_route_config,
     })
     .await
     {