[puncsky]

Summary

Map an image cron's --cron-command to the existing Docker command override, as image cron creation already does. Keep native-only build commands and incompatible registry credentials refused.

Motivation

The update builder currently rejects cron-command together with build-command, preventing an ordinary image cron command replacement or clear.

How to verify

go test ./cmd/... ./pkg/... ./internal/...

• All 57 development packages pass on the candidate.
• Builder tests cover replacement, explicit empty clearing, omission during a schedule-only update, and the existing build-command / registry-credential refusals.
• New-code lint is clean against c31e586e; full lint on unmodified main reports 92 pre-existing findings with the pinned golangci-lint v2.14.0.

Release notes

Image-backed cron jobs accept cron-command updates and explicit command clearing.