fix(post): align microformat block with PostEntry types for svelte-check

Three CI typecheck failures from the previous microformat patch:

- post.created is the only date field in the schema (no _created on the
  generated PostEntry). Drop the _created fallback.
- postTag items can be a slug string OR a tag object. Type narrowing
  with `'name' in tag` widened to `never`; pull the name through an
  explicit `{ name?: string }` cast in @const so the iteration stays
  honest about the runtime shape.
- author isn't on PostEntry either; cast at the use-site for the
  hidden h-card author block.

src/routes/post/[slug]/+page.svelte

@@ -78,12 +78,12 @@
   itemtype={data.isEvent ? 'https://schema.org/Event' : 'https://schema.org/BlogPosting'}
 >
   <a class="u-url" href="#" aria-hidden="true" hidden></a>
-  {#if data.post._created || data.post.created}
+  {#if data.post.created}
     <time
       class="dt-published"
-      datetime={String(data.post.created ?? data.post._created ?? '')}
+      datetime={String(data.post.created)}
       hidden
-    >{data.post.created ?? data.post._created}</time>
+    >{data.post.created}</time>
   {/if}
   {#if data.contentHeadlineHtml}
     <div class="content markdown max-w-none prose prose-zinc p-name">
@@ -121,15 +121,19 @@
   {/if}
   {#if (data.post.postTag ?? []).length > 0}
     <div hidden>
-      {#each data.post.postTag ?? [] as tag}
-        {#if tag && typeof tag === 'object' && 'name' in tag && tag.name}
-          <span class="p-category">{tag.name}</span>
+      {#each (data.post.postTag ?? []) as tag}
+        {@const tagName =
+          tag && typeof tag === 'object'
+            ? ((tag as { name?: string }).name ?? '')
+            : ''}
+        {#if tagName}
+          <span class="p-category">{tagName}</span>
         {/if}
       {/each}
     </div>
   {/if}
   <div class="p-author h-card" hidden>
-    <span class="p-name">{data.post.author ?? 'Bürgerinitiative Vachdorf'}</span>
+    <span class="p-name">{(data.post as { author?: string }).author ?? 'Bürgerinitiative Vachdorf'}</span>
   </div>
 </article>