feat(setup-git): add setup-git action and changelog utility scripts

actions/setup-git/action.yml

@@ -0,0 +1,24 @@
+name: "Setup Git"
+description: "Configure git user identity for automated commits"
+
+inputs:
+  user-name:
+    description: "Git user.name"
+    required: false
+    default: "github-actions[bot]"
+  user-email:
+    description: "Git user.email"
+    required: false
+    default: "github-actions[bot]@users.noreply.github.com"
+
+runs:
+  using: "composite"
+  steps:
+    - name: "Configure git identity"
+      run: |
+        git config user.name "$GIT_USER_NAME"
+        git config user.email "$GIT_USER_EMAIL"
+      shell: bash
+      env:
+        GIT_USER_NAME: ${{ inputs.user-name }}
+        GIT_USER_EMAIL: ${{ inputs.user-email }}

src/extract-release-notes.ts

@@ -0,0 +1,28 @@
+import * as core from '@actions/core';
+import { readFileSync } from 'node:fs';
+
+let changelog: string;
+
+try {
+  changelog = readFileSync('CHANGELOG.md', 'utf8');
+} catch {
+  core.setFailed('Could not read CHANGELOG.md');
+  process.exit(1);
+}
+
+const lines = changelog.split('\n');
+const firstHeader = lines.findIndex((line) => /^## /.test(line));
+
+if (firstHeader === -1) {
+  core.setFailed('No release section (## heading) found in CHANGELOG.md');
+  process.exit(1);
+}
+
+const secondHeader = lines.findIndex((line, index) => index > firstHeader && /^## /.test(line));
+
+const notes = lines
+  .slice(firstHeader + 1, secondHeader === -1 ? undefined : secondHeader)
+  .join('\n')
+  .trim();
+
+core.setOutput('release_details', notes);

src/validate-changelog.ts

@@ -0,0 +1,15 @@
+import * as core from '@actions/core';
+import { readFileSync } from 'node:fs';
+
+let changelog: string;
+
+try {
+  changelog = readFileSync('CHANGELOG.md', 'utf8');
+} catch {
+  core.setFailed('Could not read CHANGELOG.md');
+  process.exit(1);
+}
+
+if (!/##\s+UNRELEASED/i.test(changelog)) {
+  core.setFailed('UNRELEASED section not found in CHANGELOG.md');
+}