jobq: Scheduler::new_job is gone

It handed out exactly the builder JobBuilder::new is pub(crate) to
withhold, which was agreed against more than once. I had left it in
place with a docstring naming it as the hole and folded the fix into an
open question. It was not an open question.

It only survived because two hive-c0re tests minted a builder by hand to
simulate a MetaLock growing its cascade. The grown thing is a template,
so the fix is the same as for the deploy graft and the reconcile
fan-out: call it.

exec.rs's MetaLock arm looped rebuild_nodes inline -- the second and last
construction site declaring nodes inside an executor. It is now
templates::grown_rebuilds, so a test can assert what a sweep declares by
calling the same function production calls.

grown_subgraph_roots_on_emitter_and_rebases_local_deps and
meta_update_grows_cascade_in_dag differed only in RebuildOpts; they are
one test over the declared shape, checking a root chain per agent, a
build each, and a drain each because a boot sweep is graceful.

With those gone, CompleteNode::new_job, CompleteNode::complete_node_growing
and drain_meta_syncs had no callers either. hive-jobq's own two growth
tests use JobBuilder::new() directly -- in-crate, so the wall holds.
grep for new_job across the workspace now returns nothing.

hive-c0re/src/job_queue/exec.rs

@@ -72,11 +72,7 @@ pub(super) async fn run_node(
             inputs,
         } => run_meta_lock(coord, *sweep, fanout.clone(), inputs)
             .await
-            .map(|(agents, opts)| {
-                for agent in agents {
-                    super::templates::rebuild_nodes(&job, &agent, opts, None);
-                }
-            }),
+            .map(|(agents, opts)| super::templates::grown_rebuilds(&job, &agents, opts)),
         NodeKind::Reconcile { .. } => run_reconcile(coord, agent).await.map(|sub| {
             if let Some(kind) = sub {
                 super::templates::fanned_out_mechanical(&job, kind);