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.

CLAUDE.md

@@ -242,8 +242,11 @@ read them à la carte.
   endpoint authenticate a pushing hive, and what does a snapshot
   actually contain?"** →
   [`docs/snapshot-store.md`](docs/snapshot-store.md).
-- **"How does the rebuild queue work? What are queue kinds and sources?"** →
-  [`docs/coordinator.md`](docs/coordinator.md).
+- **"What am I looking at in the build queue? What does each step
+  mean?"** → [`docs/jobq.md`](docs/jobq.md) (operator-facing, no
+  implementation detail).
+- **"How does the rebuild queue work internally? What are queue kinds and
+  sources?"** → [`docs/coordinator.md`](docs/coordinator.md).
 - **"How does the CI runner work? What's the auto-registration flow?"** →
   [`docs/ci.md`](docs/ci.md).
 - **"What is `/knowledge`? How does the hive-wide knowledge repo sync,