feat(hive-c0re): replace rebuild queue with generic job-DAG queue

jobs are now DAGs of primitive nodes (prebuild, stop-for-update, swap,
reconcile, signal, drain, ...) driven by one scheduler with N build
slots + per-agent lifecycle leases. per-agent power intent (wanted
up/offline) is durable in agent_power.sqlite; Reconcile nodes converge
observed state to it. kills the graceful-stop watcher thread, the
deferred-start follow-up, and the cascade pre-enqueue (fan-out on
MetaLock completion instead). tracker: #2166

hive-c0re/Cargo.toml

@@ -18,6 +18,7 @@ clap-markdown = "0.1"
 hive-sh4re.workspace = true
 libc.workspace = true
 listenfd = "1"
+petgraph.workspace = true
 rusqlite.workspace = true
 serde.workspace = true
 serde_json.workspace = true