perf: content-visibility on snippets + stable min-heights (M6/M7)

M6: content-visibility:auto + contain-intrinsic-size on each snippet wrapper so
off-screen snippets skip layout/paint (helps the many-frameworks worst case).
M7: give the code editor body a min-height (h-40) and fix the loading skeleton's
invalid h-164px to a matching h-40 so the skeleton->code swap doesn't shift (CLS).

Author: matschik

src/lib/components/CodeEditor.svelte

@@ -52,7 +52,7 @@
 <div class="relative group">
   <div
     bind:this={codeSnippetEl}
-    class="bg-[#0d1117] px-4 py-3 text-sm overflow-auto rounded-b rounded-tr"
+    class="bg-[#0d1117] min-h-40 px-4 py-3 text-sm overflow-auto rounded-b rounded-tr"
   >
     {#if snippet}
       <!-- eslint-disable-next-line svelte/no-at-html-tags -->

src/lib/components/Comparison.svelte

@@ -278,6 +278,7 @@
                   {#each snippets.filter((s) => s.sectionId === section.sectionId) as snippet (snippet.snippetId)}
                     {@const snippetPathId = section.sectionId + "." + snippet.snippetId}
                     <div
+                      class="snippet-cv"
                       id={snippetPathId}
                       data-snippet-id={snippetPathId}
                       data-testid={`snippet-${snippetPathId}`}
@@ -391,7 +392,7 @@
                                         class="h-2.5 rounded-full bg-gray-700 w-10 animate-pulse"
                                       ></div>
                                     </div>
-                                    <div class="w-full h-164px bg-[#0d1117] px-4 py-7">
+                                    <div class="w-full h-40 bg-[#0d1117] px-4 py-7">
                                       <div class="max-w-sm animate-pulse">
                                         <div class="h-3.5 rounded-full bg-gray-700 w-48 mb-4"></div>
                                         <div
@@ -448,4 +449,12 @@
   .header-anchor:hover > a {
     opacity: 1;
   }
+
+  /* M6: skip layout/paint for off-screen snippets (big DOMs with many
+     frameworks). `auto` remembers the real size once measured; the estimate is
+     a first-paint placeholder. The sticky title lives inside and keeps working. */
+  .snippet-cv {
+    content-visibility: auto;
+    contain-intrinsic-size: auto 600px;
+  }
 </style>