chore: ignore local .codex/ agent tooling directory (#1579)

The Codex CLI writes a local .codex/config.toml into the repo root. It's
per-developer tooling, not project source, so add it to .gitignore.

Co-authored-by: Jack Zhuang <277994282+os-zhuang@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: 3 people

.gitignore

@@ -114,4 +114,7 @@ apps/cloud/artifacts/
 studio-crm.png
 examples/app-crm/storage/
 
-.objectstack
+.objectstack
+
+# Local agent tooling
+.codex/