feat: add release workflow and update contributing guidelines for version tagging and GitHub releases

.github/workflows/release.yml

@@ -0,0 +1,52 @@
+name: Release
+
+# Pushing a tag like v0.2.0 creates its GitHub release, with that version's CHANGELOG.md section as
+# the notes. Run it by hand (Actions → Release → Run workflow) for a tag that was pushed before
+# this workflow existed. Packagist picks up tags on its own; this only adds the GitHub release.
+
+on:
+  push:
+    tags: [ "v*" ]
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: Existing tag to create a release for, e.g. v0.1.0
+        required: true
+
+permissions:
+  contents: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ inputs.tag || github.ref }}
+
+    - name: Release notes from CHANGELOG.md
+      env:
+        TAG: ${{ inputs.tag || github.ref_name }}
+      run: |
+        version="${TAG#v}"
+        # The lines between "## [<version>]" and the next "## [" heading
+        awk -v v="$version" '
+          index($0, "## [" v "]") == 1 { found = 1; next }
+          found && /^## \[/ { exit }
+          found { print }
+        ' CHANGELOG.md > notes.md
+        if [ ! -s notes.md ]; then
+          echo "::error::CHANGELOG.md has no section for ${version}"
+          exit 1
+        fi
+
+    - name: Create the GitHub release
+      env:
+        GH_TOKEN: ${{ github.token }}
+        TAG: ${{ inputs.tag || github.ref_name }}
+      run: |
+        # Tags with a suffix (v1.0.0-rc.1) are pre-releases, like Composer treats them
+        prerelease=""
+        case "$TAG" in *-*) prerelease="--prerelease" ;; esac
+        gh release create "$TAG" --title "Mygra ${TAG}" --notes-file notes.md --verify-tag $prerelease

CONTRIBUTING.md

@@ -45,6 +45,13 @@ composer analyse   # PHPStan, level 6
 
 `composer.lock` is committed and resolved for PHP 8.1 (`config.platform.php`), so every CI job installs the same versions. After changing dependencies, run `composer update` and commit the lock file.
 
+## Releasing
+
+1. Move the changes under a new `## [x.y.z] - YYYY-MM-DD` heading in `CHANGELOG.md` (and add its link at the bottom). Merge to `main` with CI green.
+2. Tag and push: `git tag -a vx.y.z -m "Mygra x.y.z" && git push origin vx.y.z`.
+
+Packagist publishes the tag on its own, and the Release workflow creates the GitHub release with that version's CHANGELOG section as its notes. A tag with a suffix (`v1.0.0-rc.1`) becomes a pre-release.
+
 ## License
 
 By contributing to this project, you agree to license your contribution under the MIT license.