ci: add shellcheck workflow, install/uninstall scripts

.github/workflows/shellcheck.yml

@@ -0,0 +1,23 @@
+name: ShellCheck
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+permissions:
+  contents: read
+
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install ShellCheck
+        run: sudo apt-get install -y shellcheck
+
+      - name: Run ShellCheck on all hooks
+        run: |
+          shellcheck pre-commit commit-msg pre-push post-checkout post-commit post-merge