fix: remove shutdown_flag param to run_login_server() (#2399)

In practice, this was always passed in as `None`, so eliminated the
param and updated all the call sites.

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* __->__ #2399
* #2398
* #2396
* #2395
* #2394
* #2393
* #2389

codex-rs/tui/src/onboarding/auth.rs

@@ -281,7 +281,7 @@ impl AuthModeWidget {
     fn start_chatgpt_login(&mut self) {
         self.error = None;
         let opts = ServerOptions::new(self.codex_home.clone(), CLIENT_ID.to_string());
-        let server = run_login_server(opts, None);
+        let server = run_login_server(opts);
         match server {
             Ok(child) => {
                 let auth_url = child.auth_url.clone();