Pass Fathom site ID env var to Next.js build in CI

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

Author: micahwalter

.github/workflows/deploy.yml

@@ -47,6 +47,8 @@ jobs:
 
       - name: Build Next.js app
         run: npm run build
+        env:
+          NEXT_PUBLIC_FATHOM_SITE_ID: ${{ secrets.NEXT_PUBLIC_FATHOM_SITE_ID }}
 
       - name: Configure AWS credentials using OIDC
         uses: aws-actions/configure-aws-credentials@v4