Improve social media OG/Twitter meta for posts

- Fix bug: post page was overriding og:image with 150x200 thumbnail
- og:type = "article" for posts (was always "website")
- article:published_time, article:modified_time, article:author, article:tag
- og:image:alt + twitter:image:alt (post headline)
- twitter:label1/data1 with reading time
- Remove thumbnail fallback from socialImage (falls back to site logo instead)

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

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

@@ -14,15 +14,6 @@
   let { data }: { data: PageData } = $props();
 </script>
 
-<svelte:head>
-  <title>{data.seoTitle}</title>
-  {#if data.seoDescription}
-    <meta name="description" content={data.seoDescription} />
-  {/if}
-  {#if data.postImageUrl}
-    <meta property="og:image" content={data.postImageUrl} />
-  {/if}
-</svelte:head>
 
 <div class="my-4 md:flex md:items-start md:gap-4">
   {#if data.rawPostImageUrl}