Use per-pattern OG images in slug page meta tags

Replace hardcoded social-card.png with dynamic {{ogImage}} token
pointing to og/{category}/{slug}.png for each pattern page.
All locales share the same English OG image.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: brunoborges

html-generators/generate.java

@@ -487,6 +487,7 @@ String generateHtml(Templates tpl, Snippet s, Map<String, Snippet> all, Map<Stri
             Map.entry("supportBadge", supportBadge(s.supportState(), extraTokens)),
             Map.entry("supportBadgeClass", supportBadgeClass(s.supportState())),
             Map.entry("canonicalUrl", canonicalUrl),
+            Map.entry("ogImage", "%s/og/%s/%s.png".formatted(BASE_URL, s.category(), s.slug())),
             Map.entry("flatUrl", "%s/%s.html".formatted(BASE_URL, s.slug())),
             Map.entry("titleJson", jsonEscape(s.title())), Map.entry("summaryJson", jsonEscape(s.summary())),
             Map.entry("categoryDisplayJson", jsonEscape(s.catDisplay())),

templates/slug-template.html

@@ -25,15 +25,15 @@
   <meta property="og:type" content="article">
   <meta property="og:site_name" content="java.evolved">
   <meta property="og:locale" content="{{ogLocale}}">
-  <meta property="og:image" content="https://javaevolved.github.io/images/social-card.png">
+  <meta property="og:image" content="{{ogImage}}">
   <meta property="og:image:width" content="1200">
   <meta property="og:image:height" content="630">
   <meta property="og:image:type" content="image/png">
 
   <meta name="twitter:card" content="summary_large_image">
   <meta name="twitter:title" content="{{title}} | java.evolved">
   <meta name="twitter:description" content="{{summary}}">
-  <meta name="twitter:image" content="https://javaevolved.github.io/images/social-card.png">
+  <meta name="twitter:image" content="{{ogImage}}">
 
   <script type="application/ld+json">
   {