docs(CLAUDE.md): add coordinator.md entry (follow-up to #928)

CLAUDE.md

@@ -327,6 +327,9 @@ docs/
                        env vars, matrix federation pointer
   ci.md                hive-ci Forgejo Actions runner: options, container
                        shape, auto-registration flow, nix sandbox note
+  coordinator.md       rebuild queue: queue kinds (Rebuild, MetaUpdate, Spawn),
+                       dedup logic, sources, cascade tracking, step labels;
+                       serialisation rationale
 ```
 
 ## Reading paths
@@ -364,6 +367,8 @@ read them à la carte.
 - **"How do I connect two hives into a swarm? How do I declare peer
   hives and configure TLS trust?"** →
   [`docs/swarm.md`](docs/swarm.md).
+- **"How does the rebuild queue work? What are queue kinds and sources?"** →
+  [`docs/coordinator.md`](docs/coordinator.md).
 
 ## Conventions & process