fix(keeld): log the effective ambient cadence, not the raw setting

A settings.json predating the ambient fields deserializes cadence to 0;
the sentinel clamps that to its 5m default, so log the clamped value
instead of a misleading cadence=0s.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/keeld/main.go

@@ -150,6 +150,13 @@ func main() {
 	if ambMode == "" {
 		ambMode = settings.AmbientNotify
 	}
+	// Compute the effective cadence so the log reflects what the sentinel will
+	// actually use: New clamps a non-positive value (e.g. a settings.json that
+	// predates these fields) to a default, mirrored here for the log line.
+	ambCadence := time.Duration(cfg.AmbientCadenceSecs) * time.Second
+	if ambCadence <= 0 {
+		ambCadence = 5 * time.Minute
+	}
 	sentinel := ambient.New(ambient.Deps{
 		AI:         base.AI,
 		Knowledge:  base.Knowledge,
@@ -158,8 +165,8 @@ func main() {
 		Memory:     base.Memory,
 		Clock:      time.Now,
 		ActiveMode: func() string { return h.State().ActiveMode },
-	}, time.Duration(cfg.AmbientCadenceSecs)*time.Second, ambMode)
-	log.Printf("ambient: mode=%s cadence=%ds", ambMode, cfg.AmbientCadenceSecs)
+	}, ambCadence, ambMode)
+	log.Printf("ambient: mode=%s cadence=%s", ambMode, ambCadence)
 
 	srv := web.NewServer(h)
 	srv.Init() // re-arm or expire a restored deadline-bearing session