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/+layout.svelte

@@ -52,6 +52,14 @@
     seoTitle?: string;
     seoDescription?: string;
     socialImage?: string;
+    ogType?: string;
+    ogImageAlt?: string;
+    articlePublishedTime?: string | null;
+    articleModifiedTime?: string | null;
+    articleAuthor?: string | null;
+    articleTags?: string[];
+    twitterLabel1?: string;
+    twitterData1?: string;
     robots?: string;
     keywords?: string;
     preview?: boolean;
@@ -218,7 +226,7 @@
     {/if}
     <link rel="canonical" href={canonical} />
     <!-- Open Graph -->
-    <meta property="og:type" content="website" />
+    <meta property="og:type" content={pageData?.ogType ?? "website"} />
     <meta property="og:url" content={canonical} />
     <meta property="og:title" content={seoTitle} />
     {#if seoDescription}
@@ -228,9 +236,24 @@
       <meta property="og:image" content={socialImageUrl} />
       <meta property="og:image:width" content={String(SOCIAL_IMAGE_DIMENSIONS.width)} />
       <meta property="og:image:height" content={String(SOCIAL_IMAGE_DIMENSIONS.height)} />
+      {#if pageData?.ogImageAlt}
+        <meta property="og:image:alt" content={pageData.ogImageAlt} />
+      {/if}
     {/if}
     <meta property="og:locale" content="de_DE" />
     <meta property="og:site_name" content={data.siteName} />
+    {#if pageData?.articlePublishedTime}
+      <meta property="article:published_time" content={pageData.articlePublishedTime} />
+    {/if}
+    {#if pageData?.articleModifiedTime}
+      <meta property="article:modified_time" content={pageData.articleModifiedTime} />
+    {/if}
+    {#if pageData?.articleAuthor}
+      <meta property="article:author" content={pageData.articleAuthor} />
+    {/if}
+    {#each pageData?.articleTags ?? [] as tag}
+      <meta property="article:tag" content={tag} />
+    {/each}
     <!-- Twitter -->
     <meta name="twitter:card" content="summary_large_image" />
     <meta name="twitter:url" content={canonical} />
@@ -240,6 +263,13 @@
     {/if}
     {#if socialImageUrl}
       <meta name="twitter:image" content={socialImageUrl} />
+      {#if pageData?.ogImageAlt}
+        <meta name="twitter:image:alt" content={pageData.ogImageAlt} />
+      {/if}
+    {/if}
+    {#if pageData?.twitterLabel1 && pageData?.twitterData1}
+      <meta name="twitter:label1" content={pageData.twitterLabel1} />
+      <meta name="twitter:data1" content={pageData.twitterData1} />
     {/if}
     <!-- JSON-LD WebSite + Organization -->
     {@html jsonLdScript}