TLS 1.3, channel persistence, membership signaling

- TLS 1.3 on TCP (rustls + tokio-rustls, optional self-signed cert)
- Server-side channel CRUD with SQLite persistence
- Gateway → voice-node membership bridge via broadcast channel

serverd/Cargo.toml

@@ -21,3 +21,4 @@ tracing-subscriber.workspace = true
 anyhow.workspace             = true
 toml.workspace               = true
 serde.workspace              = true
+serde_json.workspace         = true