Add ShellCheck and Ruff code sniffers to CI and release workflows

- Introduce dedicated ShellCheck workflow for Bash scripts
- Add Ruff as Python code sniffer for src/ and tests/
- Integrate both sniffers into main CI pipeline
- Require successful sniffer runs before marking a release as stable
- Ensure consistent code quality checks across CI and release workflows

https://chatgpt.com/share/693d5b26-293c-800f-999d-48b2950b9417

.github/workflows/mark-stable.yml

@@ -29,8 +29,16 @@ jobs:
   test-virgin-root:
     uses: ./.github/workflows/test-virgin-root.yml
 
+  codesniffer-shellcheck:
+    uses: ./.github/workflows/codesniffer-shellcheck.yml
+
+  codesniffer-ruff:
+    uses: ./.github/workflows/codesniffer-ruff.yml
+
   mark-stable:
     needs:
+      - codesniffer-shellcheck
+      - codesniffer-ruff
       - test-unit
       - test-integration
       - test-env-nix