feat: Task Health Check + customer_number in webhook payload

- Task model: CustomerNumber field (K-Nummer aus customers.number)
- DB: taskSelectCols joined c.number, scanTask scans CustomerNumber
- Hub: WaitForAgentOnline() polls until agent reconnects or timeout
- Scheduler: executeUpdateWithHealthCheck() waits for agent reconnect after update
  - health_check: {agent_online: bool, checked_at: RFC3339} in result
  - Status: completed_with_warning wenn Update OK aber Agent offline bleibt
- Frontend: Task-Tabelle zeigt Status-Badge (lauft/fehler/warnung/abgebr.)

backend/db/tasks.go

@@ -126,14 +126,14 @@ func scanTask(scan func(dest ...interface{}) error) (*models.Task, error) {
 	var startedAt, finishedAt, lastRun, nextRun sql.NullTime
 	var resultJSON sql.NullString
 	var webhookURL, webhookResponse, createdBy sql.NullString
-	var agentName, customerName sql.NullString
+	var agentName, customerName, customerNumber sql.NullString
 	var name, scheduleType, scheduleTime sql.NullString
 	var scheduleWeekday, scheduleMonthday sql.NullInt32
 	var reboot, healthCheck, active sql.NullBool
 	var healthCheckTimeout, runCount sql.NullInt32
 
 	err := scan(
-		&t.ID, &t.AgentID, &agentName, &customerName,
+		&t.ID, &t.AgentID, &agentName, &customerName, &customerNumber,
 		&name, &t.Action, &t.Status, &scheduledAt, &startedAt, &finishedAt,
 		&resultJSON, &webhookURL, &t.WebhookSent, &webhookResponse,
 		&createdBy, &createdAt,
@@ -146,6 +146,7 @@ func scanTask(scan func(dest ...interface{}) error) (*models.Task, error) {
 
 	t.AgentName = agentName.String
 	t.CustomerName = customerName.String
+	t.CustomerNumber = customerNumber.String
 	t.Name = name.String
 	t.ScheduleType = scheduleType.String
 	if t.ScheduleType == "" {
@@ -208,7 +209,7 @@ func scanTask(scan func(dest ...interface{}) error) (*models.Task, error) {
 	return &t, nil
 }
 
-const taskSelectCols = `t.id, t.agent_id, COALESCE(a.name, ''), COALESCE(c.name, ''),
+const taskSelectCols = `t.id, t.agent_id, COALESCE(a.name, ''), COALESCE(c.name, ''), COALESCE(c.number, ''),
 	t.name, t.action, t.status, t.scheduled_at, t.started_at, t.finished_at,
 	t.result, t.webhook_url, t.webhook_sent, t.webhook_response,
 	t.created_by, t.created_at,
@@ -415,6 +416,12 @@ func (d *Database) CancelTask(id int) error {
 	return nil
 }
 
+// UpdateTaskStatusDirect sets only the status field (for post-completion overrides).
+func (d *Database) UpdateTaskStatusDirect(id int, status string) error {
+	_, err := d.db.Exec("UPDATE tasks SET status = $1 WHERE id = $2", status, id)
+	return err
+}
+
 func (d *Database) DeleteTask(id int) error {
 	res, err := d.db.Exec("DELETE FROM tasks WHERE id = $1", id)
 	if err != nil {