Increase social link spacing further, add About-me divider

Sidebar gap 6rem -> 10rem (previous doubling still read as too small).
About-me page: add a subtle .social-links-divider <hr> between the bio
text and the icon row (8rem gap above it, 3rem below to the icons) -
11rem total separation from the text, up from 3rem, plus a visual
break as requested.

static/css/site.css

@@ -392,9 +392,9 @@ ul.menuitems {
   justify-content: center;
   gap: 0.75rem;
   list-style: none;
-  /* At least double the standard 3rem inter-section gap (e.g. the gap
-     above "Tags:") to set the icon row apart from the sidebar nav. */
-  margin: 6rem 0 0 0;
+  /* Clearly more than double the standard 3rem inter-section gap (e.g.
+     the gap above "Tags:") to set the icon row apart from the sidebar nav. */
+  margin: 10rem 0 0 0;
 }
 
 .social-links li {
@@ -420,7 +420,9 @@ ul.menuitems {
   height: 1.25rem;
 }
 
-/* About-me page variant: bigger icons, distinct gap from the text above. */
+/* About-me page variant: bigger icons, distinct gap from the text above.
+   Spacing to the preceding text is handled by .social-links-divider's
+   own margins, so this only needs the gap from divider to icons. */
 .social-links--large {
   margin-top: 3rem;
   gap: 1.5rem;
@@ -431,6 +433,13 @@ ul.menuitems {
   height: 5rem;
 }
 
+.social-links-divider {
+  border: none;
+  border-top: 1px solid var(--table-border-color);
+  width: 4rem;
+  margin: 8rem auto 0 auto;
+}
+
 
 .menuitems {
   list-style: none;

templates/page.html

@@ -20,6 +20,7 @@
     {{ page.content }}
 
     {% if page.slug == 'about-me' %}
+    <hr class="social-links-divider">
     {% set social_links_variant = 'large' %}
     {% include "includes/social_links.html" %}
     {% endif %}