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/src/voice_membership.rs

@@ -0,0 +1,22 @@
+use tokio::sync::broadcast;
+
+#[derive(Clone, Debug)]
+pub enum VoiceMembershipEvent {
+    Joined {
+        channel_id: String,
+        session_id: String,
+        user_id: String,
+    },
+    Left {
+        channel_id: String,
+        session_id: String,
+        user_id: String,
+    },
+}
+
+pub fn voice_membership_channel() -> (
+    broadcast::Sender<VoiceMembershipEvent>,
+    broadcast::Receiver<VoiceMembershipEvent>,
+) {
+    broadcast::channel(256)
+}