client: add password-stdin flag with U2F enforcement

[BetaFold3]

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.

[BetaFold3]

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.

[BetaFold3]

@rgooch @cviecco Friendly ping! Just checking if there's any feedback on this PR or if you'd like me to make any adjustments to the approach?

The CI failures from last time appear to be infrastructure-related as all tests pass locally. Happy to address any concerns or suggestions you might have.