ci: add gitleaks secret-scan workflow

.github/workflows/secret-scan.yml

@@ -0,0 +1,40 @@
+name: Secret Scanning
+
+on:
+  pull_request:
+  push:
+    branches: [main, master]
+
+permissions:
+  contents: read
+
+jobs:
+  secret-scan:
+    name: Gitleaks Secret Scan
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Install Gitleaks
+        run: |
+          VERSION=$(curl -sI https://github.com/gitleaks/gitleaks/releases/latest | grep -i '^location:' | sed 's/.*tag\/v//' | tr -d '\r')
+          curl -sSfL "https://github.com/gitleaks/gitleaks/releases/download/v${VERSION}/gitleaks_${VERSION}_linux_x64.tar.gz" | tar xz
+          chmod +x gitleaks
+
+      - name: Scan for secrets
+        run: |
+          if [ "${{ github.event_name }}" = "pull_request" ]; then
+            ./gitleaks detect --source . --log-opts "${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }}" --verbose
+          else
+            BEFORE="${{ github.event.before }}"
+            if [ "$BEFORE" = "0000000000000000000000000000000000000000" ]; then
+              # Branch creation push -- no prior SHA. Scan full tree.
+              ./gitleaks detect --source . --verbose
+            else
+              ./gitleaks detect --source . --log-opts "${BEFORE}..${{ github.sha }}" --verbose
+            fi
+          fi