ci: add dependabot auto-merge with reviewer fallback

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

@@ -0,0 +1,45 @@
+name: Dependabot auto-merge
+
+on: pull_request_target
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  auto-merge:
+    name: Auto-merge Dependabot PRs
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    timeout-minutes: 5
+
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v3
+
+      - name: Enable auto-merge for patch updates
+        if: 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 }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for minor development updates
+        if: |
+          steps.metadata.outputs.update-type == 'version-update:semver-minor' &&
+          steps.metadata.outputs.dependency-type == 'direct:development'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Request review for non-low-risk updates
+        if: |
+          steps.metadata.outputs.update-type == 'version-update:semver-major' ||
+          (steps.metadata.outputs.update-type == 'version-update:semver-minor' &&
+           steps.metadata.outputs.dependency-type != 'direct:development')
+        run: gh pr edit "$PR_URL" --add-reviewer ronload
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}