Initial commit: split VNOX monorepo into VNOX-Server

Unified server binary (vnox-serverd) combining:
- Gateway (TCP, auth, channels, sessions, SQLite)
- Voice-node (UDP relay, Opus, jitter buffer)

Standalone gateway (vnox-gateway) and voice-node (vnox-voice-node) preserved as sub-crates.

gateway/src/handler/friends/decline.rs

@@ -0,0 +1,37 @@
+use anyhow::Result;
+use tokio::net::TcpStream;
+
+use crate::{
+    domain::session,
+    net::io,
+    proto::{FriendDeclinePayload, PacketId, SessionCrypto, to_payload},
+};
+
+pub async fn handle_friend_decline(
+    stream: &mut TcpStream,
+    seq: &mut u32,
+    session_id: &str,
+    payload: &[u8],
+    crypto: &SessionCrypto,
+    state: &crate::net::state::State,
+) -> Result<()> {
+    let req: FriendDeclinePayload = serde_json::from_slice(payload)?;
+    let sess = session::get(&state.sessions, session_id)
+        .await
+        .ok_or_else(|| anyhow::anyhow!("session not found"))?;
+
+    state
+        .storage
+        .decline_friend_request(&req.from_user_id, &sess.user_id)
+        .await?;
+
+    io::send_encrypted(
+        stream,
+        PacketId::FriendDecline,
+        seq,
+        &to_payload(&serde_json::json!({"status": "DECLINED"})),
+        crypto,
+    )
+    .await?;
+    Ok(())
+}