fix: bound agent workflow overhead

[baokhang83]

Summary

• replace free-form generated product diagrams with a bounded native renderer that owns layout, arrows, theming, and iframe height
• give agents explicit knowledge-record flags while retaining compact syntax compatibility
• align Claude and Codex skill guidance with the public FluencyLoop commands and the low-cost diagram path

Verification

• shellcheck and Bash syntax checks
• Node syntax check
• bats tests/add-knowledge.bats tests/diagram-renderer.bats tests/plugin.bats tests/cli.bats tests/calibration.bats tests/check.bats