docs(swarm): address review

swarm-controller/README.md "What it does" was still missing two route
groups argus caught: linked external matrix/forge accounts
(PUT .../matrix-accounts/{account}, .../forge-accounts/{label}) and
config-PR status (GET /api/config-prs, /api/agents/{name}/config-pr).
Verified against the router at main.rs:2874-2899.

swarm-controller/README.md

@@ -28,6 +28,13 @@ The swarm's control plane. The swarm UI and `swarmctl` are its clients.
 - **Agent credentials** — at start and every five minutes it re-checks every
   agent's forge token and matrix account, and renews store certificates and
   queue secrets as they age.
+- **Linked external accounts** — an operator-supplied matrix or forge
+  account for one agent, stored in the swarm secret store
+  (`PUT /api/hives/{hive}/agents/{agent}/matrix-accounts/{account}`,
+  `.../forge-accounts/{label}`); distinct from the agent's own swarm-minted
+  accounts above.
+- **Config PR status** — each agent's open config-repo PR, cached from forge
+  webhooks (`GET /api/config-prs`, `/api/agents/{name}/config-pr`).
 - **Swarm-wide forge objects and webhooks** →
   [`docs/swarm/README.md`](../docs/swarm/README.md#swarm-wide-forge-objects).
 - **Relays** — each agent's terminal and turn-state header as SSE, agent