refactor(PageTransition): optimize layer management and transition handling

src/components/common/PageTransition.scss

@@ -14,6 +14,7 @@
     gap: $spacing-lg;
     min-height: 0;
     flex: 1;
+    background: var(--bg-secondary);
     backface-visibility: hidden;
     transform: translateZ(0);
 
@@ -21,7 +22,6 @@
     &--exit {
       position: absolute;
       inset: 0;
-      z-index: 1;
       overflow: hidden;
       pointer-events: none;
       will-change: transform, opacity;
@@ -38,6 +38,5 @@
 
   &--animating &__layer:not(.page-transition__layer--exit) {
     position: relative;
-    z-index: 0;
   }
 }