ci(.gitlab-ci): add GitLab runner

: title

.gitlab-ci.yml

+---
+image: python:3.13-slim
+
+stages:
+  - prebuild
+  - build
+  - deploy
+  - deploy-pages
+
+variables:
+  PIPELINE_VERSION: 1.0.0
+  PREBUILD_OUTPUT: "output"
+  BUILD_OUTPUT: "output/public"
+
+prebuild:
+  before_script:
+    - apt-get update && apt-get install -y pandoc python3-pip
+    - python3 -m pip install poetry
+    - pandoc -v
+    - poetry --version
+  stage: prebuild
+  script: |
+    echo "Working directory: $(pwd)"
+    ls -la
+    # Run the build script
+    ./build.sh
+  artifacts:
+    paths:
+      - $PREBUILD_OUTPUT
+    expire_in: "1 hour"
+
+build:
+  image: ubuntu:24.04
+  stage: build
+  cache:
+    key: decker-cache
+    paths:
+      - .cache/decker/
+    policy: pull-push
+  before_script:
+    - mkdir -p .cache/decker
+    - |
+      if [ ! -f .cache/decker/decker ]; then
+        echo "Downloading decker..."
+        apt-get update && apt-get install -y curl
+        curl -L -o .cache/decker/decker https://github.com/decker-edu/decker/releases/download/latest/decker-latest-Linux-X64-3f4150d61ca167361b02665da969da769ca98e7c
+        chmod +x .cache/decker/decker
+      else
+        echo "Using cached decker binary"
+      fi
+  dependencies:
+    - prebuild
+  script: |
+    ls .cache
+    cd $PREBUILD_OUTPUT
+    ls -a ../.cache/decker
+    ls -a
+    ../.cache/decker/decker decks
+  artifacts:
+    paths:
+      - $BUILD_OUTPUT
+    expire_in: "1 hour"
+
+deploy:
+  stage: deploy
+  dependencies:
+    - build
+  script:
+    - mkdir -p public
+    - cp -r $BUILD_OUTPUT/* public/
+  artifacts:
+    paths:
+      - public
+
+deploy-pages:
+  stage: deploy-pages
+  only:
+    - main
+  dependencies:
+    - deploy
+  script:
+    - ls -a public
+  pages: true