fix(websocket): lossless EOF signal + pending sweep (WS-02, CON-02)

- Replace the axum/tungstenite pump paths' Notify-based read-EOF signal
  with a retained tokio watch channel: a late subscriber (monitor
  spawned after session setup, or pump EOF before the receiver is
  taken) still observes EOF (WS-02).
- from_wss drop monitor: on EOF (or session close) fail all pendings
  retryable, then keep sweeping the pending map every 1 s — calls
  registered after the initial fail_all (the forgotten-session import
  path) resolve instead of hanging (CON-02).
- Tests: drop-during-registration race variants (forget + held
  session) and a post-EOF registration resolved via the sweep; the
  existing no-hang test stays green.

cargo test (219), cargo test --features wss (231, 3x for flake check),
cargo clippy --all-targets -- -D warnings, cargo fmt --check

src/websocket/upgrade.rs

@@ -97,6 +97,13 @@ fn install_channel_zero(
     })
 }
 
+#[allow(dead_code)]
+pub(crate) fn adapter_install_channel_zero(
+    registry: Arc<OperationRegistry>,
+) -> alkcall::channels::adapter::InstallChannelZero {
+    install_channel_zero(registry)
+}
+
 struct NoopProvider;
 
 impl alkcall::core::auth::IdentityProvider for NoopProvider {