aider: Updated the reference to highlight_image in default.html t…

…o use `page.highlight_image`.

# Aider chat conversation:

USER: in default.html, how should i reference the `highlight_image` declared in the markdown front matter?

ASSISTANT: To reference the `highlight_image` front matter variable in `default.html`, you can use the Liquid syntax `{{ page.highlight_image }}`.

Here's the change in a *SEARCH/REPLACE block*:

_layouts/default.html
<source>html
<<<<<<< SEARCH
    {% if highlight_image %}
    <meta property="og:image" content="{{ site.url }}{{ highlight_image }}">
=======
    {% if page.highlight_image %}
    <meta property="og:image" content="{{ site.url }}{{ page.highlight_image }}">
>>>>>>> REPLACE
</source>

This checks if `page.highlight_image` is defined in the front matter of the current page. If so, it sets the `og:image` meta tag to the full URL of the highlight image by prepending `site.url` to `page.highlight_image`.

_layouts/default.html

@@ -4,8 +4,8 @@
     <meta charset="UTF-8">
 
     {% seo %}
-    {% if highlight_image %}
-    <meta property="og:image" content="{{ site.url }}{{ highlight_image }}">
+    {% if page.highlight_image %}
+    <meta property="og:image" content="{{ site.url }}{{ page.highlight_image }}">
     {% else %}
     <meta property="og:image" content="{{ site.url }}/assets/aider.jpg">
     {% endif %}