docs: add swarm.md — multi-hive peer config guide

CLAUDE.md

@@ -322,6 +322,9 @@ docs/
                        firewall + federation, provisioning flow, fluffychat-web build
   network.md           host-side bridge + dnsmasq resolver, v1/v2 roadmap,
                        foundation for netns isolation
+  swarm.md             multi-hive swarm config: peer declaration, TLS trust
+                       (CA vs certFingerprint), bilateral setup, identity
+                       env vars, matrix federation pointer
 ```
 
 ## Reading paths
@@ -356,6 +359,9 @@ read them à la carte.
   [`docs/matrix.md`](docs/matrix.md).
 - **"How does DNS resolution work in agent containers? What's the
   bridge network for?"** → [`docs/network.md`](docs/network.md).
+- **"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).
 
 ## Conventions & process