fix(storage): spacing between the enrichment tag row and action rows

The .drive-agent-extra slot stacked the agent tag row and the agent
action row with no vertical gap (and sat flush against the registry
action row). The slot is now a flex column with a .6rem gap + top
margin, hidden when empty; enrichCard's inline margin removed.

controller/internal/web/templates/storage.html

@@ -328,7 +328,7 @@ window.__registeredPaths=[{{range .StoragePaths}}{{if .Path}}"{{.Path}}",{{end}}
   function enrichCard(d, registered){
     var slot=document.getElementById('agent-extra-'+regKey(d));
     if(!slot) return false;
-    var extra='<div class="metarows" style="margin:.4rem 0 0">'
+    var extra='<div class="metarows">'
       +'<span class="metarow">'+roleTag(d.role)+'</span>'
       +(d.class?'<span class="metarow">'+classTag(d)+'</span>':'')
       +(d.durable_id?'<span class="metarow mono" title="Tartós azonosító">'+esc(d.durable_id)+'</span>':'')