Describe the feature or enhancement

In the Visitors > Operating System panel of the analytics dashboard, there is no icon shown for the (Unknown) OS entry. All other OS entries have an accompanying icon (e.g., Windows, Linux, macOS, etc.), but (Unknown) does not.

This results in a slight inconsistency in the UI.

Steps to Reproduce
Go to the dashboard for a site with diverse traffic sources.

Open the Operating System section under Visitors.

Observe the list — (Unknown) OS lacks an icon.

Expected Behavior
A placeholder icon (e.g. ❓ or 🖥️) should be shown next to the (Unknown) label to maintain visual consistency.

Suggested Fix
Add a default "unknown OS" icon to the icon mapping logic in the frontend.