fix: surface expired auth as AuthRequired

[kocaemre]

Summary

• Return ACP AuthRequired for terminal Codex auth failures even when a session had credentials configured.
• Keep configured non-auth failures, such as usage limits, on the existing InternalError path.
• Add regressions for expired configured ChatGPT credentials and terminal HTTP 401 responses.

Closes #495

Test Plan

• npm test -- src/__tests__/CodexACPAgent/auth-error-events.test.ts -t 'AuthRequired|configured non-auth'
• npm test -- src/__tests__/CodexACPAgent/auth-error-events.test.ts
• npm run typecheck
• npm run build
• git diff --check
• npm test

Note: Claude Code delegation was unavailable in this cron shell because claude auth status --text reports Not logged in. Run claude auth login to authenticate.; implementation and validation were performed directly with local tests.