Feat/add giscus comments1 (#627)

### What problem were solved in this pull request?

Issue Number: close #598 

Problem:

评论框已显示，但提交时报错 "Unable to create discussion"。

原因（可能）：Giscus App 未安装在 `oceanbase/miniob` 仓库。

解决方法：
1. 打开 https://github.com/apps/giscus
2. 选择 oceanbase/miniob → 点击 Install
3. 授权 "Read and write to discussions"

安装后，功能如果生效，评论会写入 "Comments" 分类。

Author: zywoote3ture

docs/mkdocs.yml

@@ -77,6 +77,7 @@ nav:
 
 theme:
   name: material
+  custom_dir: overrides
   language: zh
   features:
     - search.highlight
@@ -143,3 +144,4 @@ extra_javascript:
     # - https://polyfill.io/v3/polyfill.min.js?features=es6
     - https://polyfill.alicdn.com/v3/polyfill.min.js?features=es6
     - https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js
+

docs/overrides/partials/content.html

@@ -0,0 +1,37 @@
+<!-- 原有页面内容 -->
+{{ page.content }}
+
+<!-- Giscus 评论区 -->
+{% if page and page.meta and page.meta.comments != false %}
+  {# 可选：如果 MD 文件开头有 --- comments: false ---，则隐藏 #}
+{% endif %}
+<h2 id="__comments">讨论区</h2>
+<div class="giscus"></div>
+
+<!-- Giscus 脚本 -->
+<script src="https://giscus.app/client.js"
+        data-repo="oceanbase/miniob"
+        data-category="Comments"
+        data-mapping="pathname"
+        data-strict="0"
+        data-reactions-enabled="1"
+        data-emit-metadata="0"
+        data-input-position="bottom"
+        data-theme="preferred_color_scheme"
+        data-lang="zh-CN"
+        crossorigin="anonymous"
+        async>
+</script>
+
+<!-- 可选：自定义 CSS（嵌入 style 标签） -->
+<style>
+  .giscus {
+    margin-top: 2em;
+    border: 1px solid #e1e4e8;
+    border-radius: 8px;
+  }
+  .giscus-frame {
+    width: 100%;
+    height: 500px;  /* 可调整高度 */
+  }
+</style>