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.

style.css

@@ -708,6 +708,7 @@ img { max-width: 100%; height: auto; vertical-align: middle; }
   border-color: var(--brass);
   box-shadow: var(--shadow-hover);
 }
+.blog-thumb { display: block; width: 100%; aspect-ratio: 16/9; object-fit: cover; border-radius: 0.5rem; margin-bottom: 0.75rem; }
 .blog-card-top { display: flex; align-items: center; gap: 0.5rem; margin-bottom: 0.75rem; flex-wrap: wrap; }
 .blog-badge {
   display: inline-block; padding: 0.2rem 0.6rem; border-radius: 3rem;