ci: add dependabot auto-merge for minor/patch updates (#34)

Automatically approves and enables auto-merge on dependabot PRs
for semver minor and patch version bumps when CI passes.
Major version bumps still require manual review.

Co-authored-by: Nick Bianchi <nick@jeanarlene.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

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

@@ -0,0 +1,36 @@
+name: Dependabot auto-merge
+
+on: pull_request_target
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+        with:
+          github-token: "${{ secrets.GITHUB_TOKEN }}"
+
+      - name: Approve minor and patch updates
+        if: >-
+          steps.metadata.outputs.update-type == 'version-update:semver-minor' ||
+          steps.metadata.outputs.update-type == 'version-update:semver-patch'
+        run: gh pr review --approve "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for minor and patch updates
+        if: >-
+          steps.metadata.outputs.update-type == 'version-update:semver-minor' ||
+          steps.metadata.outputs.update-type == 'version-update:semver-patch'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}