fix: replace var with const/let and add radix to parseInt in _spaceCatcher

[coderabbitai]

Summary

Pre-existing SonarCloud findings in _spaceCatcher (l2t-paper-slider.js) that were present on master before PR #51 are now surfacing in the SonarCloud diff analysis for that PR because the function was modified.

Findings

1. var declaration (SonarCloud failure): var nextPos should be const nextPos (or let if reassigned).
2. parseInt without explicit radix (SonarCloud warning): parseInt(nextPos) should be Number.parseInt(nextPos, 10).

Impact

The var finding is a SonarCloud failure (not merely a warning) and may block the quality gate on any future PR that touches this function.

Suggested fix

const nextPos = activeEl.getAttribute('aria-posinset');
if (nextPos) this.movePos(Number.parseInt(nextPos, 10) - 1);

References

• Identified during review of PR fix: handle null activeElement in _spaceCatcher AND fix: guard _moveManual and _ariaChecked against dom-repeat race AND MORE #51 (comment: fix: handle null activeElement in _spaceCatcher AND fix: guard _moveManual and _ariaChecked against dom-repeat race AND MORE #51 (comment))
• Requested by @javier-godoy