ci: add gitleaks workflow

.forgejo/workflows/gitleaks.yml

@@ -0,0 +1,28 @@
+# gitleaks secret scan - runs on every push and pull request.
+
+name: gitleaks
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  scan:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          # Full history — gitleaks needs depth to scan a commit range.
+          fetch-depth: 0
+
+      - name: install gitleaks
+        run: |
+          curl -sSL -o gl.tar.gz \
+            https://github.com/gitleaks/gitleaks/releases/download/v8.21.2/gitleaks_8.21.2_linux_x64.tar.gz
+          tar xzf gl.tar.gz gitleaks
+          chmod +x gitleaks
+          ./gitleaks version
+
+      - name: scan
+        run: |
+          ./gitleaks detect --source . --no-banner --redact --verbose