fix: harden Windows feature preconditions

[baokhang83]

Summary

• Make calibration --help succeed in Bash and PowerShell.
• Recover safely when an agent is detached at its active feature branch tip.
• Require valid one-shot knowledge records and explicit architecture/product-overview coverage at handoff.

Verification

• bats tests/calibration.bats tests/check.bats tests/plugin.bats
• shellcheck -x -P SCRIPTDIR plugins/fluencyloop/scripts/bash/calibration.sh plugins/fluencyloop/scripts/bash/check.sh

PowerShell tests were not run locally because pwsh is unavailable.