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/content/read_receipt.rs

@@ -0,0 +1,46 @@
+use anyhow::Result;
+
+use crate::{
+    domain::session,
+    net::state::{BroadcastMsg, State},
+    proto::{PacketId, ReadReceiptPayload, encode_packet, to_payload},
+};
+
+pub async fn handle_read_receipt(
+    _stream: &mut tokio::net::TcpStream,
+    seq: &mut u32,
+    session_id: &str,
+    payload: &[u8],
+    _crypto: &crate::proto::SessionCrypto,
+    state: &State,
+) -> Result<()> {
+    let req: ReadReceiptPayload = serde_json::from_slice(payload)?;
+    let sess = match session::get(&state.sessions, session_id).await {
+        Some(s) => s,
+        None => return Ok(()),
+    };
+
+    state
+        .storage
+        .update_read_receipt(&req.channel_id, &sess.user_id, &req.last_read_message_id)
+        .await?;
+
+    let broadcast_data = serde_json::json!({
+        "channel_id": req.channel_id,
+        "user_id": sess.user_id,
+        "last_read_message_id": req.last_read_message_id,
+    });
+
+    let _ = state.broadcast.send(BroadcastMsg {
+        channel_id: Some(req.channel_id),
+        exclude_session: Some(session_id.into()),
+        target_session_id: None,
+        data: encode_packet(
+            PacketId::ReadReceiptBroadcast,
+            *seq,
+            &to_payload(&broadcast_data),
+        ),
+    });
+
+    Ok(())
+}