feat(#2591): port hive-c0re job_queue onto the hive-jobq crate

Replace the in-tree scheduler with the domain-agnostic hive-jobq crate
(merged in #2615): parent-axis grouping + borrow/subtree-reservation
resource model + roll-up completion (State::Finishing).

Host adaptation:
- NodeSpec gains an explicit `parent` axis; templates declare grouping +
  sibling ordering directly (deps order execution, parent groups a subtree
  whose resource the descendants borrow).
- Rebuild is a nested two-root subtree: Prebuild (root, owns the build slot
  for the whole subtree, lease-exempt) -> StopForUpdate (child, owns the
  agent lease) -> Swap/PostSwap (children, borrow both); Reconcile is a
  separate top-level root (AfterAny Prebuild) so it survives the cancel-
  cascade of any failed step (recovery-start invariant) and converges to
  the persisted `wanted` on a fresh lease. This is the multi-root
  correction to the single-root-chain sketch: node0=root broke lease-
  exemption (hoisting the lease onto Prebuild) and recovery-reconcile
  (root failure cancels all children).
- Spawn / perm-change / power-ops (stop/start/restart) group-rooted the
  same way; per-agent power-op subgraphs stay independent roots so a
  multi-agent DAG runs them concurrently, each on its own lease.
- insert_group honours the explicit parent axis (no lease hoisting); the
  DAG terminal node deps AfterAny on every group root and runs once the
  whole op rolls up. Drop the old Graph::add_dep terminal wiring.

36/36 job_queue tests, full hive-c0re suite green, clippy --all-targets.

Cargo.toml

@@ -53,6 +53,7 @@ clap_complete = "4"
 indicatif = "0.18"
 hive-sh4re = { path = "hive-sh4re" }
 hive-agent-sock = { path = "hive-agent-sock" }
+hive-jobq = { path = "hive-jobq" }
 hive-core-agent-sock = { path = "hive-core-agent-sock" }
 hive-claude = { path = "hive-claude" }
 hive-host-sock = { path = "hive-host-sock" }