fix(TopBanner): align text-only page title with content container

Replace `container mx-auto px-6` with `container-custom` so the
headline/subheadline block (no image case) matches the main content
padding and max-width.

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

src/lib/components/TopBanner.svelte

@@ -155,7 +155,7 @@
         {/if}
       </div>
     {:else if hasPageTitle}
-      <div class="border-b border-stein-200 container mx-auto px-6 py-4">
+      <div class="border-b border-stein-200 container-custom py-4">
         {#if headlineHtml}
           <h1 class="text-2xl font-bold text-stein-900">{@html headlineHtml}</h1>
         {/if}