Fix preview download navigation; clean up context menu config

[ewrayjohnson]

What was broken: Clicking “Download” in the preview modal navigated the main window to the file URL (e.g., [/undefined/...)), breaking the app instead of triggering a download. The main toolbar download worked because it used the host’s [onDownload]; the preview bypassed it.
Why it happened: The preview download handler called [window.location.href = filePath], forcing full-page navigation and skipping the host download pipeline.
Secondary issue caught during build: Duplicate [hidden] keys in the context menu config caused a build error.
Fix: Delegate preview downloads to the host [onDownload] via [SelectionContext] and consolidate the [hidden]condition into one boolean.
Result: Preview download now behaves like the main download button—no navigation, host-controlled download; build error removed.

[Saifullah-dev]

@ewrayjohnson The navigation to an undefined/<filePath> URL happens when the filePreviewPath prop isn’t provided to the FileManager component.

That said, delegating preview downloads to the host via the onDownload callback is a much better and more consistent approach, as it aligns the preview modal behavior with the main download action and avoids full-page navigation.

I’m approving this PR — thanks for the contribution! 🙌
Please also add an entry to CHANGELOG.md so existing users are aware of this behavior change.
Make this commit with semantic release format to publish these changes to npm.