Add frontend testing stage to Jenkinsfile and update Vitest configuration for CI environments

- Introduced a new 'Test frontend' stage in the Jenkinsfile to run unit tests using Vitest in a Docker container.
- Updated Vite configuration to conditionally include client and server test projects based on the CI environment.
- Modified backend health check tests to skip execution in CI environments.
- Adjusted test for constructing backend asset URLs to reflect default behavior when no base URL is provided.

Jenkinsfile

@@ -131,6 +131,34 @@ pipeline {
       }
     }
 
+    /* Frontend: i18n (paraglide no versionado) + vitest solo proyecto "server" (Node).
+     * "client" usa @vitest/browser+Playwright: requeriría playwright install (chromium) en el contenedor.
+     * pnpm run check svelte-check se omite mientras haya deuda de tipos en el árbol; pnpm run lint alinear cuando pase. */
+    stage('Test frontend') {
+      steps {
+        sh '''
+          set -euxo pipefail
+          echo "== Test frontend (vitest —project server) =="
+          docker run --rm \
+            -e CI=true \
+            -e NODE_ENV=test \
+            -e JENKINS_URL=${JENKINS_URL} \
+            -v "$WORKSPACE:/workspace" \
+            -w /workspace/frontend \
+            node:22-bookworm \
+            bash -lc '
+              set -euxo pipefail
+              node --version
+              corepack enable
+              pnpm --version
+              pnpm install --frozen-lockfile
+              pnpm run i18n:compile
+              pnpm run test:unit -- --run
+            '
+        '''
+      }
+    }
+
     stage('Generate version') {
       steps {
         script {