client: add password-stdin flag with U2F enforcement

[tuannh99]

Add --password-stdin flag to enable secure automation workflows while maintaining strong 2FA requirements:

• Support providing password from stdin along with existing interactive prompt
• Enforce U2F as second factor
• Automatically disable TOTP and VIPAccess when using stdin
• Add tests for new functionality

Example usage with various password managers:

$ op read "op://vault-name/item-name/password" | keymaster --password-stdin -configHost ${CONFIGHOST}
$ bw get password item-id | keymaster --password-stdin -configHost ${CONFIGHOST}
$ lpass show --password item-name | keymaster --password-stdin -configHost ${CONFIGHOST}

This approach ensures physical security token presence while enabling automation.

[tuannh99]

Note: The GitHub Actions failures appear to be CI infrastructure related rather than code issues. All tests pass locally. Would appreciate a re-run of the checks when possible.