perf(core): replace lazysizes with browser-level lazy loading (#1267)

_sass/layout/post.scss

@@ -26,26 +26,6 @@
   color: var(--text-color);
 }
 
-.preview-img {
-  overflow: hidden;
-  aspect-ratio: 40 / 21;
-
-  @extend %rounded;
-
-  &:not(.no-bg) {
-    img.lazyloaded {
-      background: var(--img-bg);
-    }
-  }
-
-  img {
-    -o-object-fit: cover;
-    object-fit: cover;
-
-    @extend %rounded;
-  }
-}
-
 h1 + .post-meta {
   > span + span::before {
     @include dot;
@@ -368,10 +348,6 @@ h1 + .post-meta {
 }
 
 @media all and (max-width: 576px) {
-  .preview-img[data-src] {
-    margin-top: 2.2rem;
-  }
-
   .post-tail-bottom {
     flex-wrap: wrap-reverse !important;
 
@@ -396,9 +372,4 @@ h1 + .post-meta {
     margin-left: -0.5rem;
     margin-right: -0.5rem;
   }
-
-  .preview-img[data-src] {
-    max-width: 100vw;
-    border-radius: 0;
-  }
 }