Is it permissible to seek a fatwa without the husband's knowledge to avoid his anger?

There is no objection to your asking about religious matters without your husband's knowledge. However, avoid delving deeply into issues that may lead to waswasah (obsessive whispering/doubt), as excessive questioning is blameworthy in Islamic law and a waste of time. The Companions used to ask the Prophet, peace and blessings be upon him, about real-life matters that benefited them, not about hypothetical situations or complex issues.