Complete Phase 5.1.1: Comprehensive CSS performance optimization

- Removed unused CSS rules: eliminated redundant height utilities and duplicate responsive rules in utilities.css
- Optimized CSS selectors: confirmed efficient BEM architecture and class-based selectors throughout codebase
- Implemented hardware acceleration: added backface-visibility, perspective, transform:translateZ(0), and will-change properties to animated components (messages, buttons) for GPU acceleration
- Maintained performance: preserved only essential utilities while ensuring browser compatibility

Related to task 5.1.1 in UI_UPDATE.MD: CSS Optimization for UI rendering performance.

static/css/components.css

@@ -1636,6 +1636,26 @@ a:focus-visible {
     opacity: 1;
 }
 
+/* Hardware acceleration for animations */
+.message {
+    backface-visibility: hidden;
+    perspective: 1000px;
+    transform: translateZ(0);
+    will-change: opacity, transform;
+}
+
+.message.selected {
+    backface-visibility: hidden;
+    perspective: 1000px;
+    transform: translateZ(0);
+}
+
+.message-actions {
+    backface-visibility: hidden;
+    perspective: 1000px;
+    transform: translateZ(0);
+}
+
 .message-actions {
     position: absolute;
     right: 0;