Add codex permission-mode plumbing and full-yolo approval policy

Plumb an explicit permissionMode through handleCodexCommand into
runCodex via new --permission-mode and --yolo flags, and seed the
session's currentPermissionMode / dangerouslySkipPermissions from it.

Map yolo and bypassPermissions to the 'never' approval policy (was
'on-failure') so full-yolo sessions never interrupt for approvals.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>