refactor(#2825): complete_node takes only the node id

`NodeId` has been globally unique across DAGs since #2801, so the dag id
carried no information the node id didn't. The parameter was already
underscore-prefixed as unused, but still populated by `claim_ready`, carried
through the scheduler's mpsc on every `Claim`, and passed at the call site —
three layers of plumbing feeding a dead argument.

Removing it surfaced four more dead things it had been keeping alive:
`settle_approval_tail`, `settle_rebuild_tail` and `drain_meta_syncs` each took
a dag id they only forwarded to `complete_node`, and one `submit` binding was
never read. Those are deleted rather than underscore-prefixed — prefixing is
what let the original argument survive this long.

`Claim.dag_id` stays: it has live consumers in the tracing spans,
`append_subgraph`'s container guard, `Ctx` for the build-log link,
`first_error`, and the approval-deploy context.

hive-c0re/src/job_queue/mod.rs

@@ -324,7 +324,7 @@ impl JobQueue {
     /// Nothing is returned: a DAG's terminal side effects are its own tail nodes
     /// ([`NodeKind::ResolveApproval`] / [`NodeKind::EmitRebuilt`]), which the
     /// scheduler claims and runs like any other node.
-    pub fn complete_node(&self, _dag_id: u64, node_id: NodeId, result: Result<(), String>) {
+    pub fn complete_node(&self, node_id: NodeId, result: Result<(), String>) {
         let mut inner = self.lock();
         // The failure reason + `finished_at` are stamped onto the graph `Node`
         // by the scheduler (the reason rides `Outcome::Failed`); no host-side