Background images, device frames, custom shadows, and watermark text
were not rendering in the right-pane preview. The preview now updates
in real time for all settings: gradient/solid/image backgrounds, macOS/
Windows/Browser frame chrome, iPhone/MacBook/iPad frame indicators,
custom shadow parameters, and watermark text overlay.
Also fixes a React StrictMode effect-ordering race where the parent
tool-page reset cleared preview state set by the child Settings
component on initial mount.
