docs: add operator-facing jobq page, dedup coordinator.md pointer

hyperhive/hyperhive#2999 asked for an operator-facing page explaining
the job queue's node kinds in the abstract, without the coordinator's
implementation detail (leases, resource windows, module layout).

Add docs/jobq.md: what a queue row/step means, a plain-language table
of every node label an operator actually sees in the dashboard
(BU1LDS/R3BU1LD QU3U3 and swarm-ui's /jobs page both render the same
graph), and a rough shape for a typical rebuild.

Wire it into docs/README.md and the root CLAUDE.md reading-paths index
alongside coordinator.md. Add a pointer from coordinator.md's job-queue
section to the new page so the two don't try to explain the same thing
twice at different levels.

docs/coordinator.md

@@ -8,6 +8,11 @@ and `docs/persistence.md`.
 
 ## Job queue
 
+**For what each step means to someone watching the dashboard, without the
+implementation detail below, see [`jobq.md`](jobq.md) instead** — this
+section stays at the internals level (module layout, scheduler mechanics,
+resource/lease semantics).
+
 Every container/meta operation (rebuild, meta-update, first-spawn, power
 changes) is submitted to the global job-DAG queue (`hive-c0re/src/job_queue/`)
 as a **DAG of primitive nodes**. One scheduler task drives all DAGs;