Fix backend path for Vercel build

Author: prazgaitis

apps/web/vercel-build.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-cd ../packages/backend
+cd ../../packages/backend
 
 npx convex deploy \
   --cmd "export NEXT_PUBLIC_CONVEX_URL=\"$NEXT_PUBLIC_CONVEX_URL\"; export NEXT_PUBLIC_CONVEX_SITE_URL=$(printf %s \"$NEXT_PUBLIC_CONVEX_URL\" | sed 's/\\.convex\\.cloud/.convex.site/'); cd ../../apps/web && npx next build" \