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.

[kocaemre]

Rebased this PR onto current main and resolved the auth-error handling conflict against the newer session-failure flow.

Verification on the rebased head ad79bc4792b1bf655dc02dc55a130ac07a3e1af5:

• npm ci
• npm run test -- src/__tests__/CodexACPAgent/auth-error-events.test.ts -t 'AuthRequired|retryable HTTP 401|configured non-auth|ACP login error' — 8 passed / 53 skipped
• npm run test -- src/__tests__/CodexACPAgent/auth-error-events.test.ts — 61 passed
• npm run typecheck
• npm run build
• git diff --check upstream/main..HEAD

gh pr view now reports the PR as OPEN / MERGEABLE / UNSTABLE; there are no checks reported on main for this repo.