fix: bypass codex inner sandbox in sandboxes

[samuelclay]

Summary

• launch Codex app-server with the explicit externally-sandboxed bypass flag by default
• keep an env var escape hatch to re-enable Codex's inner bwrap sandbox
• update wrapper tests for the new launch command

Testing

• uv run pytest tests/test_codex_app_wrapper.py (from services/api)
• uv run ruff check ../sandbox/codex-app-wrapper.py tests/test_codex_app_wrapper.py (from services/api)
• docker build --target sandbox -t centaur-agent:latest -f services/sandbox/Dockerfile .
• docker run --rm --entrypoint codex centaur-agent:latest --dangerously-bypass-approvals-and-sandbox app-server --help
• docker run --rm --entrypoint /bin/bash centaur-agent:latest -lc 'python3 - <<'''PY'''
  import importlib.machinery
  import importlib.util
  loader = importlib.machinery.SourceFileLoader(wrapper, /usr/local/bin/codex-app-wrapper)
  spec = importlib.util.spec_from_loader(wrapper, loader)
  mod = importlib.util.module_from_spec(spec)
  loader.exec_module(mod)
  print(mod._codex_app_server_command(high))
  PY'