Round float values in webhook payloads to 1 decimal place

Webhook alert payloads now round Value and Threshold fields to 1 decimal
place before template rendering. This eliminates excessive precision in
webhook messages (e.g., 62.27451680630036 becomes 62.3).

The fix is applied in prepareWebhookData() so all webhook templates
benefit automatically, including Google Space webhooks, generic JSON
webhooks, and custom templates.

Related to #619

internal/notifications/notifications.go

@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"math"
 	"net/http"
 	"net/url"
 	"os/exec"
@@ -1615,6 +1616,10 @@ func (n *NotificationManager) prepareWebhookData(alert *alerts.Alert, customFiel
 		ackTime = alert.AckTime.Format(time.RFC3339)
 	}
 
+	// Round Value and Threshold to 1 decimal place for cleaner webhook payloads
+	roundedValue := math.Round(alert.Value*10) / 10
+	roundedThreshold := math.Round(alert.Threshold*10) / 10
+
 	return WebhookPayloadData{
 		ID:                 alert.ID,
 		Level:              string(alert.Level),
@@ -1624,8 +1629,8 @@ func (n *NotificationManager) prepareWebhookData(alert *alerts.Alert, customFiel
 		Node:               alert.Node,
 		Instance:           instance,
 		Message:            alert.Message,
-		Value:              alert.Value,
-		Threshold:          alert.Threshold,
+		Value:              roundedValue,
+		Threshold:          roundedThreshold,
 		ValueFormatted:     formatMetricValue(alert.Type, alert.Value),
 		ThresholdFormatted: formatMetricThreshold(alert.Type, alert.Threshold),
 		StartTime:          alert.StartTime.Format(time.RFC3339),