feat: See Also includes in-text links to other blog posts

Adds seeAlsoLinks filter that extracts all internal blog.giersig.eu
links from the raw markdown source and merges them with the explicit
`related` frontmatter field, deduplicated. The section now surfaces
automatically whenever an article links to another post inline.

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

_includes/layouts/post.njk

@@ -128,12 +128,13 @@ withBlogSidebar: true
   </details>
   {% endif %}
 
-  {# See Also — related posts from frontmatter (resolved wikilinks → URLs) #}
-  {% if related and related.length > 0 %}
+  {# See Also — explicit related: frontmatter + in-text links to other blog posts #}
+  {% set _seeAlso = page.inputPath | seeAlsoLinks(related) %}
+  {% if _seeAlso.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">
-      {% for relUrl in related %}
+      {% for relUrl in _seeAlso %}
       {% set _relPost = collections.posts | postByUrl(relUrl) %}
       <li>
         <a href="{{ relUrl }}" class="text-sm text-accent-700 dark:text-accent-300 hover:underline">

eleventy.config.js

@@ -1119,6 +1119,26 @@ export default function (eleventyConfig) {
     return (posts || []).find((p) => p.url === path || p.url === `${path}/`);
   });
 
+  // Collect all internal blog links from a post's raw markdown and merge with
+  // the explicit `related` frontmatter URLs. Returns a deduplicated list.
+  eleventyConfig.addFilter("seeAlsoLinks", function (inputPath, relatedUrls) {
+    const seen = new Set();
+    const result = [];
+    const add = (url) => {
+      const key = String(url).replace(/\/$/, "");
+      if (!seen.has(key)) { seen.add(key); result.push(String(url)); }
+    };
+    for (const url of (relatedUrls || [])) add(url);
+    try {
+      const content = readFileSync(inputPath, "utf-8");
+      const escaped = siteUrl.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+      const re = new RegExp(`\\]\\((${escaped}/[^)\\s]+)\\)`, "g");
+      let m;
+      while ((m = re.exec(content)) !== null) add(m[1]);
+    } catch { /* ignore */ }
+    return result;
+  });
+
   // Strip garden/* tags from a category list so they don't render as
   // plain category pills alongside the garden badge.
   eleventyConfig.addFilter("withoutGardenTags", (categories) => {