fix: per-event delete button, Docker network default, polling interval duration parsing

- Add per-event delete button (trash icon on hover) in event log entries
- Set Docker network default to 'docker-watcher' in DB schema + migration for existing DBs
- Parse Go duration strings (5m, 1h) to seconds in settings UI, convert back on save
- Clear error when network is empty in deployer instead of hidden fallback

internal/deployer/deployer.go

@@ -286,6 +286,9 @@ func (d *Deployer) executeDeploy(
 	d.logDeploy(deployID, "Image pulled successfully", "info")
 
 	// Step 2: Ensure network exists.
+	if settings.Network == "" {
+		return containerID, proxyRouteID, instanceID, fmt.Errorf("docker network not configured in settings")
+	}
 	networkID, err := d.docker.EnsureNetwork(ctx, settings.Network)
 	if err != nil {
 		return containerID, proxyRouteID, instanceID, fmt.Errorf("ensure network: %w", err)