client: keep sessionwatch out of the wasm build

The wasm client never runs the engine's session-warning flow, so linking
the full sessionwatch package (timers, event composition) only bloats the
binary. Put the watcher behind a sessionDeadlineWatcher interface and split
the constructor by build tag: !js wires the real sessionwatch.Watcher, js
gets a no-op stub that still mirrors the deadline into the status recorder
(so the Status snapshot stays correct) but drops the timers. Removes the
sessionwatch package from the wasm dependency graph.

client/internal/engine_sessionwatch_js.go

@@ -0,0 +1,39 @@
+//go:build js
+
+package internal
+
+import (
+	"time"
+
+	"github.com/netbirdio/netbird/client/internal/peer"
+)
+
+// noopSessionWatcher is the js/wasm stand-in for sessionwatch.Watcher. The
+// wasm client never runs the engine's session-warning flow (the interactive
+// T-WarningLead notification and the T-FinalWarningLead fallback dialog live
+// in the desktop UI), so linking the full sessionwatch package (timers, event
+// composition) would only bloat the binary.
+//
+// It still mirrors the deadline into the status recorder so the SubscribeStatus
+// / Status snapshot the UI consumes stays correct — only the timer-driven
+// warnings are dropped.
+type noopSessionWatcher struct {
+	recorder *peer.Status
+}
+
+func newSessionWatcher(recorder *peer.Status) sessionDeadlineWatcher {
+	return noopSessionWatcher{recorder: recorder}
+}
+
+// Update mirrors the real watcher's recorder propagation without the timers or
+// sanity-check sentinels: a valid deadline is exposed on the status snapshot,
+// the zero time clears it.
+func (w noopSessionWatcher) Update(deadline time.Time) error {
+	if w.recorder != nil {
+		w.recorder.SetSessionExpiresAt(deadline)
+	}
+	return nil
+}
+
+func (noopSessionWatcher) Dismiss() {}
+func (noopSessionWatcher) Close()   {}