feat(#2500): scaffold hive-jobq crate with the core graph data model

First step of extracting the job-DAG queue into a domain-agnostic
`hive-jobq` library, per the operator's v2 design: one persistent
graph, named-counter resources, recursive node groups, opaque stable
node ids, guard-object locks, a slot-filling scheduler.

This commit lands only the data model, so the shape can be reviewed
before the machinery is built on it:

- NodeId: opaque, stable, monotonic; group membership is a parent
  edge, not encoded in the id (the 1/1/2 hierarchy is a derived UI
  label).
- ResourceName, Dep (Node | Resource{name,count}), State.
- Node<N>: caller-defined payload N so the library stays
  container-agnostic.
- Graph<N>: insert (mints stable ids), node lookup, children,
  recursive group-terminal check. Retains completed groups (no
  pruning in v1).

The resource-acquisition machinery (atomic all-or-nothing acquire),
the recursive-lock guards, and the scheduler loop are follow-ups.
Tests cover id minting, group terminality, and state terminality;
clippy + rustdoc clean.

Cargo.lock

@@ -1662,6 +1662,14 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "hive-jobq"
+version = "0.1.0"
+dependencies = [
+ "serde",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "hive-matrix-mcp"
 version = "0.1.0"