ci: Add multi-arch Docker build/publish and tagged release workflow

Build and push linux/amd64 + linux/arm64 images to GHCR on every push
to master and on v* tags. On v* tags, also generate a changelog from
conventional commits and create a GitHub release.

.github/generate_changelog.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Usage: ./generate_changelog.sh [<git-log-range>]
+#
+# Groups commits by their conventional-commit prefix (feat, fix, ...) into
+# sections. Commits within each section are sorted oldest-first. Commits
+# that don't match a known prefix land in an "Other" section.
+
+range="${1:-}"
+
+types="feat fix refactor perf docs test ci build chore"
+
+label_for() {
+  case "$1" in
+    feat) echo "Features" ;;
+    fix) echo "Fixes" ;;
+    refactor) echo "Refactoring" ;;
+    perf) echo "Performance" ;;
+    docs) echo "Documentation" ;;
+    test) echo "Tests" ;;
+    ci) echo "CI" ;;
+    build) echo "Build" ;;
+    chore) echo "Chores" ;;
+    *) echo "Other" ;;
+  esac
+}
+
+commits=$(git log ${range} --reverse --pretty='format:%s')
+known_pattern="^(feat|fix|refactor|perf|docs|test|ci|build|chore): "
+
+first_section=1
+for type in $types other; do
+  if [ "$type" = "other" ]; then
+    entries=$(printf '%s\n' "$commits" | grep -v -E "$known_pattern" | sed 's/^/- /' || true)
+  else
+    entries=$(printf '%s\n' "$commits" | grep -E "^${type}: " | sed -E "s/^${type}: /- /" || true)
+  fi
+
+  [ -z "$entries" ] && continue
+  [ "$first_section" -eq 0 ] && echo
+  first_section=0
+
+  printf '### %s\n\n%s\n' "$(label_for "$type")" "$entries"
+done

.github/workflows/docker-publish.yml

@@ -0,0 +1,88 @@
+name: Docker build & release
+
+on:
+  push:
+    branches: [master]
+    tags: ["v*"]
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=sha,format=short
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=raw,value=latest,enable=${{ startsWith(github.ref, 'refs/tags/v') }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+  release:
+    needs: build-and-push
+    if: startsWith(github.ref, 'refs/tags/v')
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Generate changelog
+        id: changelog
+        run: |
+          prev_tag=$(git describe --tags --abbrev=0 "${{ github.ref_name }}^" 2>/dev/null || true)
+          if [ -n "$prev_tag" ]; then
+            range="${prev_tag}..${{ github.ref_name }}"
+          else
+            range=""
+          fi
+          .github/generate_changelog.sh "$range" > /tmp/changelog.md
+          cat /tmp/changelog.md
+
+      - name: Create GitHub release
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh release create "${{ github.ref_name }}" \
+            --title "${{ github.ref_name }}" \
+            --notes-file /tmp/changelog.md