Website: Wrap navbar when there is not enough space (#6541)

## What's the problem this PR addresses?

When there isn't enough horizontal space, the scrollbar appears for the
navbar.

Fixes #6070
Fixes #6537

## How did you fix it?

Wraps the navbar instead if there isn't enough horizontal space. The
[VSCode website](https://code.visualstudio.com/) does that too so it
isn't like out of the way either


https://github.com/user-attachments/assets/a7ed8307-d9df-4539-af21-59856ffe6463


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packages/docusaurus/src/css/custom.css

@@ -111,6 +111,14 @@ html.blog-wrapper .container {
 
 .navbar {
   top: -1px;
+  height: auto;
+}
+
+.navbar__items {
+  flex: 1 0 min-content;
+}
+.navbar__items--right {
+  margin-left: auto;
 }
 
 .navbar__brand {