ci: auto-approve dependabot PRs

Allows dependabot PRs to auto-merge without manual review while
still requiring reviews for human PRs.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jgeluk

.github/workflows/dependabot-approve.yml

@@ -0,0 +1,17 @@
+name: Auto-approve Dependabot
+
+on: pull_request_target
+
+permissions:
+  pull-requests: write
+
+jobs:
+  approve:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Approve Dependabot PR
+        run: gh pr review --approve "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}