fix: <img> aspect ratio w/ height: auto

Complement with `max-width: 100%` with a `height: auto` to preserve `<img>` aspect ratios, particularly when it's not wrapped in a block parent e.g. `<p>` or `<figure>` most commonly.

Related: https://www.smashingmagazine.com/2020/03/setting-height-width-images-important-again/

internal/ui/static/css/common.css

@@ -1038,6 +1038,10 @@ article.category-has-unread {
     max-width: 100%;
 }
 
+.entry-content img {
+    height: auto;
+}
+
 .entry-content figure {
     margin-top: 15px;
     margin-bottom: 15px;