feat: introduce CI/CD runner

Installs dependencies, checks style, runs tests.

ref: N25B-366

.gitlab-ci.yml

@@ -0,0 +1,40 @@
+# ---------- GLOBAL SETUP ---------- #
+workflow:
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+
+stages:
+  - install
+  - lint
+  - test
+
+variables:
+  NODE_VERSION: "24.11.1"
+  BASE_LAYER: trixie-slim
+
+default:
+  image: docker.io/library/node:${NODE_VERSION}-${BASE_LAYER}
+
+# --------- INSTALLING --------- #
+install:
+  stage: install
+  tags:
+    - install
+  script:
+    - npm ci
+
+# ---------- LINTING ---------- #
+lint:
+  stage: lint
+  tags:
+    - lint
+  script:
+    - npm run lint
+
+# ---------- TESTING ---------- #
+test:
+  stage: test
+  tags:
+    - test
+  script:
+    - npm run test