Update changelogs from fern repo (#3319)

Co-authored-by: patrickthornton <70873350+patrickthornton@users.noreply.github.com>

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2026-01-27.mdx

@@ -0,0 +1,22 @@
+## 2.18.1
+**`(fix):`** While most `<`s and `>`s should be escaped to `&lt;` and `&gt;` to avoid mangling the output,
+genuine XML/HTML tags should be kept as-is; this commit scans for potential valid tags and
+prevents their being escaped. (Ambiguous cases are escaped.)
+
+Before:
+```
+/// XMLDoc (C#) (Example of actual XML tags):
+/// See &lt;a href="https://example.com/docs"&gt;the docs&lt;/a&gt; for more info.
+/// Use &lt;code&gt;getValue()&lt;/code&gt; to retrieve the value.
+/// Note: when count &lt; 10 or count &gt; 100, special handling applies.
+```
+
+After:
+```
+/// XMLDoc (C#) (Example of actual XML tags):
+/// See <a href="https://example.com/docs">the docs</a> for more info.
+/// Use <code>getValue()</code> to retrieve the value.
+/// Note: when count &lt; 10 or count &gt; 100, special handling applies.
+```
+
+