Enforce managed authentication requirements locally (#37132)

## Why

Authentication restrictions must apply before stored or environment-provided credentials can be used, including during bootstrap before cloud requirements are fetched.

## What changed

- Add local `requirements.toml` allowlists for login methods and ChatGPT workspaces. Ignore these fields in cloud-provided requirements.
- Combine managed workspace allowlists with existing workspace restrictions by intersection, and fail closed when the resulting policy permits no usable login method.
- Centralize policy checks in the authentication manager so CLI, TUI, app-server, external-auth, and credential-loading paths consistently reject disallowed authentication before token hydration or network requests.

## Testing

- Cover policy composition, workspace intersection, invalid stored and external credentials, bootstrap enforcement, and login endpoint restrictions.

GitOrigin-RevId: efef22b248f3c3333e9aa55423e539efa2d2dd48

codex-rs/app-server/src/in_process.rs

@@ -403,6 +403,7 @@ async fn run_outbound_router(
 }
 
 async fn start_uninitialized(args: InProcessStartArgs) -> IoResult<InProcessClientHandle> {
+    args.config.auth_config().validate()?;
     let channel_capacity = args.channel_capacity.max(1);
     let installation_id = resolve_installation_id(&args.config.codex_home).await?;
     let (client_tx, mut client_rx) = mpsc::channel::<InProcessClientMessage>(channel_capacity);