fix: set VITE_API_URL env var in Build job

Ensures Vite sees VITE_API_URL as an empty string (not undefined) during
pnpm build, so the || window.location.origin fallback fires at runtime
instead of baking in the UAT URL.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -119,6 +119,8 @@ jobs:
         run: pnpm install --frozen-lockfile
 
       - name: Build all packages
+        env:
+          VITE_API_URL: ""
         run: pnpm build
 
   docker: