fix: add markdownlint config and auto-fix markdown errors

- Add .markdownlint-cli2.jsonc based on headlamp-agent-skills config
- Disable MD013 (line length), MD041 (first-line-heading), MD036
  (emphasis-as-heading), MD024 (no-duplicate-heading), MD040
  (fenced-code-language), MD060 (table-column-style), MD029
  (ol-prefix), MD033 (no-inline-html) — appropriate for plugin docs
- Run markdownlint-cli2 --fix to auto-fix MD022, MD031, MD032
- Manually fix remaining code block language annotations

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docs/user-guide/rbac-permissions.md

@@ -508,9 +508,11 @@ If using a log aggregator (e.g., Elasticsearch), create filters to exclude or do
    Expected: `yes`
 
 4. **Verify RoleBinding subjects match:**
+
    ```bash
    kubectl -n polaris get rolebinding headlamp-polaris-proxy -o yaml
    ```
+
    Check `subjects[].name` and `subjects[].namespace` match your Headlamp SA or user
 
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