Relocate PromotionResult into proto/fmp

Move the PromotionResult enum (and its impl) out of peer::mod and into
proto/fmp/core.rs, alongside the cross_connection_winner tie-break helper
that was relocated the same way. This is FMP connection-lifecycle result
vocabulary, so it belongs in the FMP subsystem home rather than the peer
module.

Behavior-neutral pure type relocation: consumers import it from
crate::proto::fmp, and the crate-root public path crate::PromotionResult
is preserved via a re-export in lib.rs (mirroring cross_connection_winner).
Full lib suite green at baseline.

src/node/handlers/handshake.rs

@@ -5,11 +5,11 @@ use crate::PeerIdentity;
 use crate::node::acl::PeerAclContext;
 use crate::node::reject::{HandshakeReject, RejectReason};
 use crate::node::{Node, NodeError};
-use crate::peer::{ActivePeer, PeerConnection, PromotionResult};
+use crate::peer::{ActivePeer, PeerConnection};
 use crate::proto::fmp::wire::{Msg1Header, Msg2Header, build_msg2};
 use crate::proto::fmp::{
     ConnAction, EstablishSnapshot, EstablishView, InboundDecision, InboundReject, OutboundDecision,
-    OutboundSnapshot, WireOutcome, cross_connection_winner,
+    OutboundSnapshot, PromotionResult, WireOutcome, cross_connection_winner,
 };
 use crate::transport::{Link, LinkDirection, LinkId, ReceivedPacket};
 use std::time::Duration;

src/node/tests/session.rs

@@ -1002,7 +1002,7 @@ fn build_ipv6_packet(
 
 #[test]
 fn test_identity_cache_populated_on_promote() {
-    use crate::peer::PromotionResult;
+    use crate::proto::fmp::PromotionResult;
 
     let mut node = make_node();
     let transport_id = TransportId::new(1);

src/node/tests/unit.rs

@@ -1,6 +1,6 @@
 use super::*;
 use crate::nostr::{BootstrapEvent, NostrRendezvous};
-use crate::peer::PromotionResult;
+use crate::proto::fmp::PromotionResult;
 use crate::transport::udp::UdpTransport;
 use crate::transport::{TransportHandle, packet_channel};
 use std::sync::Arc;