Expand CLI help reference

[dapi]

Summary

• add side-effect-free root, config, and update help
• derive root option help from the same global option definitions used by flag binding
• document the public help contract and record Feature Flow artifacts for Expand CLI help into a discoverable command and option reference #36

Validation

• go vet ./...
• compile-only Go test packages
• make docs-lint
• git diff --check
• go test execution is blocked locally by dyld: missing LC_UUID; required GitHub Verify CI will run the suites

Closes#36