[codex] Add automatic auth profile switch option

[zzj3720]

Summary

• add an automatic allocation mode to the session auth-profile switch endpoint
• reuse the existing weighted quota selector so manual recovery can rebind to the best usable account
• expose 自动分配 in the session account dialog and default blocked sessions to that choice

Validation

• pnpm build
• pnpm test (final rerun passed 49 files / 261 tests)

Notes

• an earlier full-suite run hit two unrelated 5s timeout flakes in app-server-process/job-manager; rerunning the suite passed completely.