FleetOperatorScore gains an Option<PublishedChart> field: None renders +
installs the chart from local source (dev/e2e, unchanged); Some installs
the published oci://<registry>/<project>/harmony-fleet-operator:<version>
chart via the same HelmChartScore (the CD "harmony apply" path).
`--operator-chart-version` selects it.
Operator chart is namespace-neutral + carries an explicit chart_version,
so one published artifact installs into any namespace at a pinned tag.
Documents the decision in ADR-012-2.
Slim variant of feat/fleet-harmony-apply: a plain Option field + inline
branch instead of an OperatorChartSource enum + builder + chart_ref()
method + unit tests.
