feat(client): read basedOnDraftVersion from the building block status

meshStack reports whether the block is on a draft version of its
definition, which lets a PUT change its parent building blocks on that
version.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: grubmeshi

client/building_block_v2.go

@@ -249,6 +249,8 @@ type MeshBuildingBlockV2Status struct {
 	// LatestDryRunUuid is the latest dry (DETECT) run, but only when it is the newest run; nil otherwise.
 	// Ungated like LatestRunUuid.
 	LatestDryRunUuid *string `json:"latestDryRunUuid" tfsdk:"latest_dry_run_uuid"`
+	// BasedOnDraftVersion is nil from a meshStack that predates the field.
+	BasedOnDraftVersion *bool `json:"basedOnDraftVersion" tfsdk:"-"`
 	// RunStartFailure says why meshStack could not start the run it was last asked for, phrased for the
 	// user, and is nil while nothing stands in the way of a run. meshStack records it, and stamps
 	// RunStartFailedOn anew, each time a request for a run fails to start one.