Parallelize frontend tests in Drone pipeline with 4 shards

Split the monolithic "build and test" kaniko step into a DAG:
tests run in 4 parallel shards (vitest --shard) alongside the
Docker image build, gated by a shared npm ci step. The kaniko
build now targets the named 'production' stage to skip the
in-Dockerfile test stage.

.drone.yml

@@ -30,8 +30,55 @@ steps:
         exit 1
       - git checkout "$DRONE_COMMIT"
 
-  - name: Build and test frontend image
+  - name: install-frontend-deps
+    image: node:24-alpine
+    depends_on:
+      - clone
+    environment:
+      NODE_OPTIONS: "--max-old-space-size=1024"
+    commands:
+      - cd frontend && npm ci
+
+  - name: test-shard-1
+    image: node:24-alpine
+    depends_on:
+      - install-frontend-deps
+    environment:
+      NODE_OPTIONS: "--max-old-space-size=1024"
+    commands:
+      - cd frontend && npx vitest run --reporter=verbose --shard=1/4
+
+  - name: test-shard-2
+    image: node:24-alpine
+    depends_on:
+      - install-frontend-deps
+    environment:
+      NODE_OPTIONS: "--max-old-space-size=1024"
+    commands:
+      - cd frontend && npx vitest run --reporter=verbose --shard=2/4
+
+  - name: test-shard-3
+    image: node:24-alpine
+    depends_on:
+      - install-frontend-deps
+    environment:
+      NODE_OPTIONS: "--max-old-space-size=1024"
+    commands:
+      - cd frontend && npx vitest run --reporter=verbose --shard=3/4
+
+  - name: test-shard-4
+    image: node:24-alpine
+    depends_on:
+      - install-frontend-deps
+    environment:
+      NODE_OPTIONS: "--max-old-space-size=1024"
+    commands:
+      - cd frontend && npx vitest run --reporter=verbose --shard=4/4
+
+  - name: build-frontend-image
     image: plugins/kaniko
+    depends_on:
+      - clone
     resources:
       limits:
         memory: 2048MiB
@@ -42,6 +89,7 @@ steps:
       repo: viktorbarzin/immoweb
       dockerfile: frontend/Dockerfile
       context: frontend
+      target: production
       enable_cache: true
       cache_repo: viktorbarzin/immoweb-cache
       tags:
@@ -50,12 +98,20 @@ steps:
 
   - name: Update deployment
     image: alpine
+    depends_on:
+      - test-shard-1
+      - test-shard-2
+      - test-shard-3
+      - test-shard-4
+      - build-frontend-image
     commands:
       - apk add curl
       - 'curl -s -X PATCH "https://kubernetes:6443/apis/apps/v1/namespaces/realestate-crawler/deployments/realestate-crawler-ui" -H "Authorization: Bearer $(cat /var/run/secrets/kubernetes.io/serviceaccount/token)" -H "Content-Type: application/json-patch+json" -k -d ''[{"op":"replace","path":"/spec/template/spec/containers/0/image","value":"viktorbarzin/immoweb:''"$DRONE_BUILD_NUMBER"''"}]'' | head'
 
   - name: verify-deploy
     image: alpine
+    depends_on:
+      - Update deployment
     commands:
       - apk add --no-cache curl jq
       - |