ci: add GitLab CI pipeline and rootfs smoke tests

- tests/: offline tree validation plus rootfs smoke tests that assert
  the hardening guarantees (kptr_restrict, default-deny firewall,
  key-only ssh, no snapd/telemetry, btrfs tooling).
- ci/: GitLab pipeline - validate, build matrix (server/workstation/
  cloud), smoke tests, publish on tags.

ci/.gitlab-ci.yml

@@ -0,0 +1,99 @@
+# ─────────────────────────────────────────────────────────────────────────────
+# Arcline OS — GitLab CI pipeline
+#
+# Mirrors the local build flow (scripts/ + Makefile) in CI:
+#   validate → build (matrix over editions) → test → publish
+#
+# The build image is Debian bookworm with the host deps installed, matching
+# what scripts/check-host-deps.sh expects locally.
+# ─────────────────────────────────────────────────────────────────────────────
+stages:
+  - validate
+  - build
+  - test
+  - publish
+
+variables:
+  DEBIAN_FRONTEND: noninteractive
+  VERSION: "0.1.0"
+
+# ── validate ────────────────────────────────────────────────────────────────
+validate:
+  stage: validate
+  image: debian:bookworm
+  script:
+    - apt-get update -qq && apt-get install -y -qq make bash
+    - make check
+
+# ── build (one job per edition) ─────────────────────────────────────────────
+.build:
+  stage: build
+  image: debian:bookworm
+  before_script:
+    - apt-get update -qq
+    - apt-get install -y -qq debootstrap squashfs-tools grub2-common xorriso cpio curl git make bash
+  script:
+    - make iso-${EDITION}
+  artifacts:
+    name: "arcline-${EDITION}-${VERSION}"
+    paths:
+      - build/artifacts/
+    expire_in: 2 weeks
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+      when: never
+    - when: always
+
+build-server:
+  extends: .build
+  variables:
+    EDITION: server
+
+build-workstation:
+  extends: .build
+  variables:
+    EDITION: workstation
+
+build-cloud:
+  extends: .build
+  variables:
+    EDITION: cloud
+
+# ── test ────────────────────────────────────────────────────────────────────
+test:
+  stage: test
+  image: debian:bookworm
+  needs: [build-server, build-workstation, build-cloud]
+  before_script:
+    - apt-get update -qq && apt-get install -y -qq bash make xz-utils
+  script:
+    # extract the rootfs artifacts so the smoke tests can inspect them
+    - for f in build/artifacts/arcline-*.tar.xz; do
+        [ -e "$f" ] || continue;
+        e=$(basename "$f" | sed -E 's/arcline-([a-z]+)-.*/\1/');
+        mkdir -p "build/rootfs/$e";
+        tar -xJf "$f" -C "build/rootfs/$e";
+      done
+    - make test
+  artifacts:
+    reports:
+      junit: build/logs/*.xml
+    when: always
+
+# ── publish (tagged releases only) ──────────────────────────────────────────
+publish:
+  stage: publish
+  image: alpine:latest
+  needs: [test]
+  before_script:
+    - apk add --no-cache curl jq
+  script:
+    - echo "Publishing release $VERSION (edit this step to push to your release server / GitLab Packages)"
+    - ls -la build/artifacts/ || true
+  artifacts:
+    name: "arcline-${VERSION}"
+    paths:
+      - build/artifacts/
+    expire_in: 1 year
+  rules:
+    - if: '$CI_COMMIT_TAG'