Fix large image overflow in comment page (#31740)

Close #31709 

52px is calculate by avatar size in
templates\repo\issue\view_content\comments.tmpl
```html
<img src="{{.Poster.AvatarLink $.Context}}" width="40" height="40">
```
+
```css
.ui.comments .comment > .avatar ~ .content {
  margin-left: 12px;
}
```


![圖片](https://github.com/user-attachments/assets/bf15f4d4-1574-46f6-9f5e-1fbdbf1a98b0)

---------

Co-authored-by: wxiaoguang <[email protected]>

Author: charles7668

Diff for: templates/repo/issue/fields/markdown.tmpl

@@ -1,3 +1,3 @@
 <div class="field {{if not .item.VisibleOnForm}}tw-hidden{{end}}">
-	<div>{{ctx.RenderUtils.MarkdownToHtml .item.Attributes.value}}</div>
+	<div class="markup">{{ctx.RenderUtils.MarkdownToHtml .item.Attributes.value}}</div>
 </div>

Diff for: web_src/css/modules/comment.css

@@ -53,6 +53,7 @@
   display: flex;
   flex-direction: column;
   flex: 1;
+  min-width: 0;
 }
 
 .ui.comments .comment > .avatar ~ .content {