fixed some style issues, added tooling for docs

docs/hosts/mgmt_msg.md

@@ -0,0 +1,19 @@
+# hosts/mgmt_msg.h
+
+## class MgmtMsg — public interface
+
+### `virtual ~MgmtMsg() = default;`
+
+## class HeartbeatMsg — public interface
+
+### `: subscriber_id(sid), status(st), generated_at(t) { ... }`
+### `MgmtKind kind() const noexcept override { ... }`
+
+## class JobFinishedMsg — public interface
+
+### `: flow_id(fid), finished_at(t) { ... }`
+### `MgmtKind kind() const noexcept override { ... }`
+
+## class EndSimulationMsg — public interface
+
+### `MgmtKind kind() const noexcept override { ... }`