jobq: a job asks for the ids it wants back

The operator's instruction on the issue was "the closure returns an array
of guids, and enqueue_job returns the node ids in that order". What was
here instead returned a HashMap of everything inserted, and no caller used
the keys: submit dropped the return, insert_group did into_values(), and
the scheduler ignored what append_subgraph handed back. The guid-keyed
lookup was dead weight, and into_values() made that Vec arbitrarily
ordered -- harmless only because nothing read it.

insert_job now takes FnOnce(&JobBuilder) -> Vec<NodeGuid> and returns the
matching ids positionally. A handle from another job is UnknownNode rather
than a silent omission: the return is positional, so a short vector would
misalign every id after it.

c0re's Declare stays FnOnce(&Job) and the wrapper names no handles in one
place, rather than ending seven templates in an empty vector -- a DAG is
addressed by its container node, which submit inserts itself. That frees
insert_group from needing every id, so the node_rt pre-seeding goes too:
NodeRuntime is one Option field and every reader already tolerated a
missing entry (entry().or_default(), get().and_then(), iter().find()).

The tests are the argument for the shape: capturing a handle through a
mutable binding to look it up in the map afterwards collapses into
returning it and destructuring the result.

CLAUDE.md

@@ -57,7 +57,8 @@ hand-maintained per-file tree drifts out of sync with the code.
 - **`hive-jobq/`** — persistent job-DAG scheduler, extracted from
   hive-c0re's in-tree `job_queue` as a domain-agnostic library. One
   persistent graph for the whole system (not a DAG per job); enqueuing
-  inserts a self-contained sub-DAG and returns its node ids. Generic over
+  inserts a self-contained sub-DAG and returns the ids of the nodes the job
+  asked for, in the order it named them. Generic over
   the node payload `N` and the resource name `R`; resource deps are named
   counting semaphores acquired all-or-nothing at node start. `hive-c0re`'s
   remaining `job_queue/` module is the c0re-specific layer *over* this