watcher: startup notification no longer says every endpoint works (closes #230)

The startup notification ended "All notification channels are working.",
but it is written once and handed to every notification endpoint before
any delivery has succeeded or failed, so the claim was never checked and
was false whenever one endpoint refused it. It now says only that it is a
test sent to every configured notification endpoint. The startup
notification test checks the whole message.

Model: opus-5-5

internal/watcher/watcher.go

@@ -1154,8 +1154,9 @@ func (w *Watcher) saveState() {
 
 // maybeSendTestNotification sends a startup status notification
 // after the first full scan completes, if SEND_TEST_NOTIFICATION
-// is enabled. The message is clearly informational ("all ok")
-// and not an error or anomaly alert.
+// is enabled. The message is informational, not an error or anomaly
+// alert. It is written before it reaches any endpoint, so it claims
+// nothing about whether the endpoints work.
 func (w *Watcher) maybeSendTestNotification(ctx context.Context) {
 	if !w.config.SendTestNotification {
 		return
@@ -1167,7 +1168,8 @@ func (w *Watcher) maybeSendTestNotification(ctx context.Context) {
 		"dnswatcher has started and completed its initial scan.\n"+
 			"Monitoring %d domain(s) and %d hostname(s).\n"+
 			"Tracking %d port endpoint(s) and %d TLS certificate(s).\n"+
-			"All notification channels are working.",
+			"This is a test notification, sent to every configured "+
+			"notification endpoint.",
 		len(snap.Domains),
 		len(snap.Hostnames),
 		len(snap.Ports),