Fetch Requirements from cloud (#10167)

Load requirements from Codex Backend. It only does this for enterprise
customers signed in with ChatGPT.

Todo in follow-up PRs:
* Add to app-server and exec too
* Switch from fail-open to fail-closed on failure

codex-rs/core/src/skills/manager.rs

@@ -88,6 +88,7 @@ impl SkillsManager {
             Some(cwd_abs),
             &cli_overrides,
             LoaderOverrides::default(),
+            None,
         )
         .await
         {