Fix IconSelect grid overflow and scroll jump

- Set maxHeight dynamically based on available viewport space
- Clamp popup horizontally to stay within viewport
- Remove max-height CSS transition that caused scroll jumps
- Auto-close popup on ancestor scroll to prevent stale positioning

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/css/components.css

@@ -618,19 +618,15 @@ textarea:focus-visible {
 .icon-select-popup {
     position: fixed;
     z-index: 10000;
-    max-height: 0;
     overflow: hidden;
     opacity: 0;
-    transition: max-height 0.2s ease, opacity 0.15s ease, margin 0.2s ease;
-    margin-top: 0;
+    transition: opacity 0.15s ease;
+    pointer-events: none;
 }
 .icon-select-popup.open {
-    max-height: 600px;
     opacity: 1;
-    margin-top: 6px;
-}
-.icon-select-popup.open.settled {
     overflow-y: auto;
+    pointer-events: auto;
 }
 
 .icon-select-grid {