feat: schedule 6h backup via GitHub Actions instead of Vercel cron

.github/workflows/backup.yml

@@ -0,0 +1,29 @@
+name: Supabase Backup to Dropbox
+
+on:
+  schedule:
+    - cron: '0 0,6,12,18 * * *'  # every 6h at 00:00, 06:00, 12:00, 18:00 UTC
+  workflow_dispatch:               # allow manual trigger from GitHub UI
+
+jobs:
+  backup:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Trigger backup endpoint
+        run: |
+          RESPONSE=$(curl -s -w "\n%{http_code}" \
+            -X GET \
+            -H "Authorization: Bearer ${{ secrets.BACKUP_SECRET }}" \
+            https://craze-data-check.vercel.app/api/backup)
+
+          HTTP_STATUS=$(echo "$RESPONSE" | tail -n1)
+          BODY=$(echo "$RESPONSE" | head -n-1)
+
+          echo "Status: $HTTP_STATUS"
+          echo "Response: $BODY"
+
+          if [ "$HTTP_STATUS" != "200" ]; then
+            echo "Backup failed with status $HTTP_STATUS"
+            exit 1
+          fi