feat: Add Mermaid.js integration to enable diagram rendering in blog posts.

Author: donglua

_includes/mermaid.html

@@ -0,0 +1,10 @@
+<script src="https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js"></script>
+<script>
+  document.addEventListener("DOMContentLoaded", function() {
+    mermaid.initialize({
+      startOnLoad: true,
+      theme: 'default',
+      flowchart: { useMaxWidth: true }
+    });
+  });
+</script>

_layouts/post.html

@@ -0,0 +1,30 @@
+---
+layout: default
+---
+<article class="post h-entry" itemscope itemtype="http://schema.org/BlogPosting">
+
+    <header class="post-header">
+        <h1 class="post-title p-name" itemprop="name headline">{{ page.title | escape }}</h1>
+        <p class="post-meta">
+            <time class="dt-published" datetime="{{ page.date | date_to_xmlschema }}" itemprop="datePublished">
+                {{ page.date | date: "%Y-%m-%d" }}
+            </time>
+            {%- if page.author -%}
+            • <span itemprop="author" itemscope itemtype="http://schema.org/Person"><span class="p-author h-card"
+                    itemprop="name">{{ page.author | escape }}</span></span>
+            {%- endif -%}
+        </p>
+    </header>
+
+    <div class="post-content e-content" itemprop="articleBody">
+        {{ content }}
+    </div>
+
+    {%- if site.disqus.shortname -%}
+    {%- include disqus_comments.html -%}
+    {%- endif -%}
+
+    <a class="u-url" href="{{ page.url | relative_url }}" hidden></a>
+</article>
+
+{% include mermaid.html %}