Fix .github/workflows setup and implement auto-merge workflow

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

@@ -0,0 +1,36 @@
+name: Auto Merge Contributor PRs
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  auto-merge:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Check only Contributors.md was modified
+        id: check-files
+        run: |
+          CHANGED=$(git diff --name-only origin/${{ github.base_ref }}...HEAD)
+          echo "Changed files: $CHANGED"
+          if [ "$CHANGED" = "Contributors.md" ]; then
+            echo "valid=true" >> $GITHUB_OUTPUT
+          else
+            echo "valid=false" >> $GITHUB_OUTPUT
+            echo "PR modifies files other than Contributors.md — skipping auto-merge."
+          fi
+
+      - name: Auto-merge PR
+        if: steps.check-files.outputs.valid == 'true'
+        run: gh pr merge --squash "${{ github.event.pull_request.number }}"
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}