UI tweaks

[hawkeye217]

• Prevent "undefined" from being displayed in searchParams string. When searchParams is undefined, the expression with a logical && evaluates to undefined. So the string ends up being /latest.jpg?cache=1717728081280undefined. This fix corrects this bug and mimics the existing code in the ResizingCameraImage component.
• Display a message when a selected review period has no motion data rather than a spinning activity indicator. Should help mitigate issues from users who look at motion review immediately after upgrading.
• Use theme colors for "no preview found" divs. text-white would go unseen on the default theme in light mode.

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