fix backend CI pipeline

Author: lnqminh3003

.github/workflows/backend.yml

@@ -1,4 +1,4 @@
-name: Build and Deploy Frontend
+name: Build and Deploy Backend
 
 on:
   push:
@@ -14,6 +14,9 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: shatter-backend
 
     steps:
       - name: Checkout code
@@ -23,7 +26,6 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: "20"
-          cache: "npm"
 
       - name: Install dependencies
         run: npm ci