Add supplied post images to two posts and to the blog overview cards

- blog/posts/odoo-19-to-20-invoice-migration-with-n8n-and-mcp.html: in-post image
  much.png + og:image
- blog/posts/track-the-oca-modules-you-actually-use.html: in-post image
  oca_module_status.png + og:image
- blog/index.json: optional "image" key on those two entries only (text splice)
- script.js: renderBlog() draws .blog-thumb only when the entry carries an image
- style.css: .blog-thumb rule
- sitemap.xml: lastmod 2026-10-24 for the invoice-migration post

Built by profile webmaster (run 20261024_094206_5c4f28, verified PROBLEMS: 0 /
node --check OK); committed by olchi after that run died on an OpenRouter 402.

script.js

@@ -373,6 +373,14 @@ var si = 0,
                     for (var i = 0; i < pagePosts.length; i++) {
                         var p = pagePosts[i];
                         var bc = badgeClass(p.area);
+                        var thumbHtml = "";
+                        if (p.image)
+                            thumbHtml =
+                                '<img class="blog-thumb" src="' +
+                                p.image +
+                                '" alt="' +
+                                p.headline +
+                                '" loading="lazy" />';
                         var agentHtml = "";
                         if (p.agent)
                             agentHtml =
@@ -381,6 +389,7 @@ var si = 0,
                                 "</span>";
                         html +=
                             '<div class="blog-card">' +
+                            thumbHtml +
                             '<div class="blog-card-top">' +
                             '<span class="blog-badge blog-badge-' +
                             bc +