fix(peer): coalesce full UI view publications

Keep one queued and one replaceable pending snapshot for remote-library and Call-to-Play views while preserving lifecycle-event FIFO delivery. Generation barriers and fenced drains prevent stale nonempty views from crossing disable or acknowledgement boundaries.

Test Plan:
- just test
- just clippy
- focused burst, lifecycle ordering, fence, repeated-barrier, and stale-view tests
- independent ordering review
- git diff --check

crates/lanspread-peer/src/services/liveness.rs

@@ -3,10 +3,8 @@
 use std::{sync::Arc, time::Duration};
 
 use futures::{StreamExt as _, stream};
-use tokio::sync::mpsc::UnboundedSender;
-
 use crate::{
-    PeerEvent,
+    PeerEventSender,
     config::{PEER_PING_IDLE_SECS, PEER_PING_INTERVAL_SECS, peer_stale_timeout},
     content_quarantine::ContentQuarantine,
     context::{NetworkServiceCtx, OperationKind},
@@ -22,7 +20,7 @@ const MAX_CONCURRENT_PINGS: usize = 8;
 /// uses `last_revision_check`; inbound and content traffic only affect
 /// `last_seen`, which remains the stale-pruning clock.
 pub async fn run_ping_service(
-    tx_notify_ui: UnboundedSender<PeerEvent>,
+    tx_notify_ui: PeerEventSender,
     ctx: NetworkServiceCtx,
 ) -> eyre::Result<()> {
     log::info!(