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/configuration.md

@@ -286,6 +286,7 @@ localStorage.removeItem('polaris-plugin-dashboard-url');
 2. Check for JavaScript errors
 3. Disable privacy mode or try different browser
 4. Check if localStorage is enabled:
+
    ```javascript
    console.log('localStorage available:', typeof localStorage !== 'undefined');
    ```