ci: add GitLab CI/CD pipeline for Docker deploy

On every push to main: builds both Docker images on the server via
docker compose up --build -d, prunes dangling images, and prints the
running container list. No registry required — shell executor runner
on the deployment server is all that's needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -0,0 +1,50 @@
+# ──────────────────────────────────────────────────────────────────────────────
+# Flight Radar — GitLab CI/CD
+#
+# PREREQUISITES (one-time setup on the server):
+#
+#   1. Install GitLab Runner
+#      https://docs.gitlab.com/runner/install/linux-manually/
+#
+#   2. Register the runner (shell executor, tag: "shell")
+#      gitlab-runner register \
+#        --url https://gitlab.com \
+#        --registration-token <YOUR_PROJECT_TOKEN> \
+#        --executor shell \
+#        --tag-list shell \
+#        --description "flight-radar-server"
+#
+#   3. Give the runner access to Docker (no sudo needed)
+#      sudo usermod -aG docker gitlab-runner
+#      sudo systemctl restart gitlab-runner
+#
+# PIPELINE BEHAVIOUR:
+#   • Triggers on every push to the default branch (main).
+#   • Builds both Docker images on the server (no registry needed).
+#   • Brings the app up with docker compose; only changed services restart.
+#   • If the build fails the old containers keep running — no downtime.
+#   • Prunes dangling images after a successful deploy.
+# ──────────────────────────────────────────────────────────────────────────────
+
+stages:
+  - deploy
+
+variables:
+  # Stable project name so containers are found across different checkout dirs
+  COMPOSE_PROJECT: flight-radar
+  # Path to compose file (relative to repo root = $CI_PROJECT_DIR)
+  COMPOSE_FILE: flight-comparator/docker-compose.yml
+
+deploy:
+  stage: deploy
+  tags:
+    - shell          # must match the tag you gave your runner at registration
+  rules:
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+  script:
+    - echo "=== Deploying commit $CI_COMMIT_SHORT_SHA to $CI_COMMIT_BRANCH ==="
+    - docker compose -f "$COMPOSE_FILE" -p "$COMPOSE_PROJECT" up --build -d --remove-orphans
+    - echo "=== Cleaning up dangling images ==="
+    - docker image prune -f
+    - echo "=== Running containers ==="
+    - docker compose -f "$COMPOSE_FILE" -p "$COMPOSE_PROJECT" ps

flight-comparator/docker-compose.yml

@@ -1,3 +1,5 @@
+name: flight-radar   # pins the project name — must match COMPOSE_PROJECT in .gitlab-ci.yml
+
 services:
   backend:
     build: