fix: align post header left edge with tags block

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

layouts/posts/single.html

@@ -10,7 +10,8 @@
 {{- define "main" -}}
 
   <!-- ── ARTICLE HEADER ────────────────────────────────────────── -->
-  <header class="gutter-x pt-36 pb-12 max-w-5xl mx-auto relative overflow-hidden">
+  <header class="gutter-x pt-36 pb-12 relative overflow-hidden">
+    <div class="max-w-5xl mx-auto">
       <!-- Faded decorative category text -->
       {{- with index .Params.categories 0 -}}
         <div
@@ -59,6 +60,7 @@
       <time class="label text-fog" datetime="{{ .Date.Format "2006-01-02" }}">
         {{- .Date.Format "January 2, 2006" -}}
       </time>
+    </div>
   </header>
 
   <!-- ── GRADIENT DIVIDER ──────────────────────────────────────── -->