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

gateway/Cargo.toml

@@ -38,3 +38,9 @@ axum  = { version = "0.8", features = ["ws"] }
 tower = "0.5"
 sqlx     = { version = "0.9", features = ["sqlite", "runtime-tokio", "tls-rustls"] }
 bitflags = "2"
+
+# TLS 1.3 support
+rustls-pki-types = "1"
+rustls = "0.23"
+tokio-rustls = "0.26"
+rcgen = "0.13"