Connect engine NetworkingManager to Bevy GossipBridge

- Engine creates GossipBridge and returns it via NetworkingStarted event
- NetworkingManager forwards incoming gossip → GossipBridge.push_incoming()
- NetworkingManager polls GossipBridge.try_recv_outgoing() → broadcasts via iroh
- Bevy inserts GossipBridge resource when networking starts
- Added Debug impl for GossipBridge

Fixes gossip layer connectivity between iroh network and Bevy sync systems.

References: #131, #132
Signed-off-by: Sienna Meridian Satterwhite <sienna@r3t.io>

crates/libmarathon/src/engine/events.rs

@@ -4,13 +4,13 @@ use crate::networking::{NodeId, SessionId, VectorClock};
 use bevy::prelude::*;
 use uuid::Uuid;
 
-/// Events that the Core Engine emits to Bevy
 #[derive(Debug, Clone)]
 pub enum EngineEvent {
     // Networking status
     NetworkingStarted {
         session_id: SessionId,
         node_id: NodeId,
+        bridge: crate::networking::GossipBridge,
     },
     NetworkingFailed {
         error: String,