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/src/handler/content/read_receipt.rs

@@ -7,7 +7,7 @@ use crate::{
 };
 
 pub async fn handle_read_receipt(
-    _stream: &mut tokio::net::TcpStream,
+    _stream: &mut (impl tokio::io::AsyncRead + tokio::io::AsyncWrite + Unpin),
     seq: &mut u32,
     session_id: &str,
     payload: &[u8],