v3.1.1 — empty router fallback

Fixed\n\n- Restore the hidden token-saver fallback when an installed companion router returns no valid primary selection for an explicit token/context task.\n- Keep trivial and ordinary prompts silent unless the router selects one primary skill.\n\n## Verified\n\n- 32/32 tests passed.\n- Fresh-HOME neutral install smoke passed.\n- GitHub Actions CI passed on commit 3698e61.