feat: improve action button visibility with explicit styling and icon rendering

- Add explicit border and background colors to action buttons for better visibility
- Ensure Lucide icons are properly rendered in action buttons with deferred safeCreateIcons call
- Adjust badge margin to prevent overlap with action buttons
- Add z-index to action buttons to ensure proper layering

frontend/style.css

@@ -838,7 +838,7 @@ select {
   color: var(--text-primary);
 }
 .tree-item > .badge-small {
-  margin-left: auto;
+  margin-left: 4px;
 }
 .tree-item.active {
   background: var(--bg-hover);
@@ -890,9 +890,9 @@ select {
   display: inline-flex;
   align-items: center;
   justify-content: center;
-  border: 1px solid transparent;
+  border: 1px solid var(--border);
   border-radius: 6px;
-  background: transparent;
+  background: var(--bg-secondary);
   color: var(--text-muted);
   cursor: pointer;
   opacity: 1;
@@ -903,6 +903,7 @@ select {
     background 140ms ease,
     border-color 140ms ease;
   flex-shrink: 0;
+  z-index: 1;
 }
 
 .tree-item-action-btn:hover,