Add GitHub Actions workflow for checking broken links

Adds a new GitHub Actions workflow that automatically runs the Mintlify link checker on pull requests to catch broken links before they're deployed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: btiernay

.github/workflows/check-links.yml

@@ -0,0 +1,18 @@
+name: Check links
+
+on: pull_request
+
+jobs:
+  check-links:
+    name: Check links
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Node
+      uses: actions/setup-node@v4
+      with:
+        node-version: "22.x"
+    - name: Install Mintlify CLI
+      run: npm i -g mint
+    - name: Run broken link checker
+      run: mint broken-links