Strip commas from tag values when building blog tag links

Some posts declare tags using a comma-separated list (e.g. `tags: ai,
mcp, agent`) instead of the space-separated form. The Liquid template
in `_layouts/post.html` then rendered links like `/blog/tag/ai,` which
return a 404. Strip commas from both the URL and the displayed tag so
the links work regardless of the separator style used in front matter.

Author: jorgembfigueira

_layouts/post.html

@@ -15,7 +15,7 @@
         <div class="post-date">
           {{ page.date | date: '%B %d, %Y' }} 
           {% if page.tags %}
-            <span class="tags">{% for tag in page.tags %}<a href="{{site.baseurl}}/blog/tag/{{ tag | downcase | replace: '.', '-' }}">#{{ tag | downcase }}</a>{% endfor %}</span>
+            <span class="tags">{% for tag in page.tags %}<a href="{{site.baseurl}}/blog/tag/{{ tag | downcase | replace: ',', '' | replace: '.', '-' }}">#{{ tag | downcase | replace: ',', '' }}</a>{% endfor %}</span>
           {% endif %}
         </div>
         <h1 class="post-title">{{ page.title }}</h1>