fix: use --exclude to skip root-relative internal links in lychee

--root-url doesn't exist; --root-dir won't match .mdx files by path.
Root-relative hrefs like /async-polling are valid Mintlify internal
links at runtime but unresolvable by lychee against local files.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: greynewell

.github/workflows/ci.yml

@@ -32,5 +32,5 @@ jobs:
             --accept 200,201,202,203,204,206,301,302,303,307,308,429
             --max-concurrency 8
             --timeout 20
-            --root-url https://docs.supermodeltools.com
+            --exclude '^/'
             README.md **/*.mdx