ci: simplify CNAME step, remove unnecessary BUILD_DIR variable

Agent-Logs-Url: https://github.com/weavefox/docs/sessions/29741506-bb7c-429b-b3d9-fed61dc46093

Co-authored-by: hustcc <7856674+hustcc@users.noreply.github.com>

Author: Copilot

.github/workflows/deploy.yml

@@ -17,8 +17,6 @@ concurrency:
 jobs:
   build:
     runs-on: ubuntu-latest
-    env:
-      BUILD_DIR: build
     steps:
       - uses: actions/checkout@v4
 
@@ -38,12 +36,12 @@ jobs:
         run: pnpm build
 
       - name: Write CNAME
-        run: echo "docs.weavefox.ai" > "${BUILD_DIR}/CNAME"
+        run: echo "docs.weavefox.ai" > build/CNAME
 
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3
         with:
-          path: ${{ env.BUILD_DIR }}
+          path: build
 
   deploy:
     environment: