CI: add code style check

Introduce a GitHub Actions workflow that automatically runs
devtools/format-code.sh on every pull request touching source files.
If formatting changes are detected, the check fails and provides clear
instructions for contributors—run the formatter locally and enable
“Allow edits from maintainers” so fixes can be applied.

This prevents code‑style drift and eliminates style‑only update noise.

.github/workflows/ci_codestyle_check.yml

@@ -0,0 +1,39 @@
+name: "Code Style Check"
+
+on:
+  pull_request:
+
+jobs:
+  style-check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Detect changed files
+        id: code_changes
+        uses: tj-actions/changed-files@v46
+        with:
+          files: |
+            **/*.c
+            **/*.h
+            devtools/format-code.sh
+
+      - name: Enforce code style
+        run: |
+          if [ "${{ steps.code_changes.outputs.any_changed }}" != "true" ]; then
+            echo "No code changes detected; skipping style check."
+            exit 0
+          fi
+          chmod +x devtools/format-code.sh
+          ./devtools/format-code.sh
+          if ! git diff --exit-code; then
+            echo "::error ::Code style violations detected."
+            echo "Contributors: to fix this, run './devtools/format-code.sh' locally"
+            echo "and push the updated commit to your branch."
+            echo "Ensure 'Allow edits from maintainers' is enabled on this PR so maintainers"
+            echo "can help apply formatting fixes if needed."
+            exit 1
+          fi
+