ci: add Dependabot auto-merge workflow for patch and minor updates

Uses pull_request_target with dependabot/fetch-metadata to auto-approve
and enable squash-merge for non-major Dependabot PRs. Major version
bumps are skipped for manual review.

Closes #41

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>

Author: SebTardif

.github/workflows/dependabot-auto-merge.yml

@@ -0,0 +1,38 @@
+name: Dependabot Auto-Merge
+
+on:
+  pull_request_target:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+concurrency:
+  group: dependabot-auto-merge-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  auto-merge:
+    name: Auto-merge Dependabot PRs
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Approve and enable auto-merge (patch/minor only)
+        if: steps.metadata.outputs.update-type != 'version-update:semver-major'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR_URL: ${{ github.event.pull_request.html_url }}
+        run: |
+          gh pr review --approve "$PR_URL"
+          gh pr merge --auto --squash "$PR_URL"
+
+      - name: Skip major updates
+        if: steps.metadata.outputs.update-type == 'version-update:semver-major'
+        run: echo "Skipping major version update — requires manual review"