feat: related posts discovery with configurable algorithm

Add related posts sidebar component, configure related: block in Hugo config,
enable readers to discover similar content.

themes/tsuki/exampleSite/hugo.yaml

@@ -29,6 +29,18 @@ markup:
     startLevel: 2
     endLevel: 4
 
+related:
+  threshold: 80
+  includeNewer: true
+  toLower: true
+  indices:
+    - name: tags
+      weight: 100
+    - name: categories
+      weight: 60
+    - name: date
+      weight: 10
+
 params:
   description: Example site for the tsuki Hugo theme.
 

themes/tsuki/hugo.yaml

@@ -1,6 +1,21 @@
 languageCode: vi
 defaultContentLanguage: vi
 
+module:
+  mounts:
+    - source: archetypes
+      target: archetypes
+    - source: assets
+      target: assets
+    - source: data
+      target: data
+    - source: i18n
+      target: i18n
+    - source: layouts
+      target: layouts
+    - source: static
+      target: static
+
 pagination:
   pagerSize: 10
   path: page
@@ -25,6 +40,18 @@ markup:
     startLevel: 2
     endLevel: 4
 
+related:
+  threshold: 80
+  includeNewer: true
+  toLower: true
+  indices:
+    - name: tags
+      weight: 100
+    - name: categories
+      weight: 60
+    - name: date
+      weight: 10
+
 params:
   search:
     enable: true
@@ -34,3 +61,4 @@ params:
   toc:
     enable: true
     minWordCount: 400
+  relatedPostsCount: 3

themes/tsuki/layouts/_partials/related-posts.html

@@ -0,0 +1,20 @@
+{{- /*
+  Related posts for single pages. Uses Hugo's built-in `Related` keyword index.
+  Requires `related:` config in site hugo.yaml — see docs/config.md.
+  Silently no-op when no relations are found.
+*/ -}}
+{{- $count := site.Params.relatedPostsCount | default 3 -}}
+{{- $related := slice -}}
+{{- if gt $count 0 -}}
+  {{- $related = first $count (site.RegularPages.Related .) -}}
+{{- end -}}
+{{- with $related -}}
+<aside class="related-posts" aria-labelledby="related-heading">
+  <h2 id="related-heading" class="related-heading">{{ i18n "relatedPosts" | default "Bài viết liên quan" }}</h2>
+  <ul class="related-list">
+    {{- range . }}
+    <li>{{ partial "post-card.html" . }}</li>
+    {{- end }}
+  </ul>
+</aside>
+{{- end -}}