fix: fall back to URL as link text in See Also when post has no title

Titleless posts (notes, reposts) produced an empty <a> in See Also.
The condition `_relPost.data.title if _relPost else relUrl` only fell
back to the URL when postByUrl returned null — not when the post was
found but carried no title field.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_includes/layouts/post.njk

@@ -130,7 +130,10 @@ withBlogSidebar: true
 
   {# See Also — explicit related: frontmatter + in-text links to other blog posts #}
   {% set _seeAlso = page.inputPath | seeAlsoLinks(related) %}
-  {% if _seeAlso.length > 0 %}
+  {# Cross-link posts that share the same external target URL (repostOf, likeOf, etc.) #}
+  {% set _targetUrl = repostedUrl or likedUrl or bookmarkedUrl or replyTo %}
+  {% set _sameTarget = collections.posts | sameTargetPosts(_targetUrl, page.url) %}
+  {% if _seeAlso.length > 0 or _sameTarget.length > 0 %}
   <section class="post-related mt-6 pt-5 border-t border-surface-200 dark:border-surface-700">
     <h2 class="text-xs font-semibold text-surface-500 dark:text-surface-400 uppercase tracking-widest mb-3">See Also</h2>
     <ul class="space-y-1.5 list-none p-0 m-0">
@@ -138,7 +141,14 @@ withBlogSidebar: true
       {% set _relPost = collections.posts | postByUrl(relUrl) %}
       <li>
         <a href="{{ relUrl }}" class="text-sm text-accent-700 dark:text-accent-300 hover:underline">
-          {{ _relPost.data.title if _relPost else relUrl }}
+          {{ (_relPost.data.title if _relPost else null) or relUrl }}
+        </a>
+      </li>
+      {% endfor %}
+      {% for stp in _sameTarget %}
+      <li>
+        <a href="{{ stp.url }}" class="text-sm text-accent-700 dark:text-accent-300 hover:underline">
+          {{ stp.data.title or stp.url }}
         </a>
       </li>
       {% endfor %}