feat(#2450): collapse the startup sweep into one inline DAG

The boot is now ONE DAG, assembled inline in submit_boot_tree — no boot_root
Noop anchor, no per-agent child DAGs, no display-only parent_id grouping: a
sweep MetaLock root (only when something is stale) that grows one rebuild
subgraph per stale agent into the same DAG (via append_subgraph, previous
commit), plus one Reconcile root per drifted agent (independent — a boot
reconcile needs no lock bump).

- submit_boot_tree builds the DagSpec inline; removed the single-use
  templates::{boot_root, startup_sweep} builders (inlined per the operator's
  "don't force single-use shapes into templates.rs" steer).
- fanout_specs simplified to the meta-update cascade path only — the startup
  sweep no longer fans out child DAGs, so its branch was dead.
- test: append_subgraph_roots_on_emitter_and_rebases_local_deps.

Vestigial after this (deliberately left as follow-ups, flagged in the PR):
NodeKind::Noop is now unconstructed (contained to hive-c0re, removable);
Template::StartupSweep is unconstructed but a hive-sh4re wire type
(frontend-coordinated removal).

hive-c0re/src/job_queue/mod.rs

@@ -219,7 +219,12 @@ impl JobQueue {
     /// contract as `append_node` (so the DAG can't roll terminal with the
     /// appended work still pending). Returns the new node ids; empty if the
     /// DAG is gone or `nodes` is empty.
-    pub fn append_subgraph(&self, dag_id: u64, nodes: Vec<NodeSpec>, dep_on: NodeId) -> Vec<NodeId> {
+    pub fn append_subgraph(
+        &self,
+        dag_id: u64,
+        nodes: Vec<NodeSpec>,
+        dep_on: NodeId,
+    ) -> Vec<NodeId> {
         if nodes.is_empty() {
             return Vec::new();
         }