Switch to "mint" theme

The "willow" theme places the logo, version select box, and light/dark
switch all side by side in a constrained space at the top of the
sidebar, which causes rendering issues for each.

In contrast, the "mint" theme places each in a page-wide top bar,
eliminating space issues.  The "mint" theme also places the search box
in that top bar, allowing more of the sidebar to appear above the fold.

Author: jonathanhefner

docs/docs.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://mintlify.com/docs.json",
-  "theme": "willow",
+  "theme": "mint",
   "name": "Model Context Protocol",
   "colors": {
     "primary": "#09090b",