Improve CN1 playground side menu dark mode, disable swipe, and add mobile responsiveness

[liannacasper]

Motivation

• Make the playground side menu behave correctly in dark mode and avoid accidental open gestures.
• Reduce the side menu footprint on desktop and provide a more usable layout on touch/mobile devices by showing preview in a tab instead of side-by-side.

Description

• Use a desktop detection helper isDesktopLayout() and keep the existing SplitPane (with the 25% editor sizing target) for desktop while switching to a tabbed container for mobile by returning a Tabs with Editor and Preview tabs.
• Disable side-menu swipe gestures globally for the playground with Toolbar.setEnableSideMenuSwipe(false) to prevent accidental triggering.
• Expand dark-mode support by adding side-menu related UIIDs (e.g. SideNavigationPanel, PlaygroundSideCommand, PlaygroundMenuSection, etc.) to the supportsDarkVariant list so menu components receive dark variants.
• Add side-menu landscape size theme constants (sideMenuSizeLandscapeInt and sideMenuSizeTabLandscapeInt) to theme.css so the menu opens narrower (approximately 25% visible width) in desktop/landscape layouts.

Testing

• Attempted to build the playground with cd scripts/cn1playground && ./build.sh but the script is not executable in this environment, so the build did not run. (failed)
• Attempted cd scripts/cn1playground && bash build.sh, but the script invokes ./mvnw which is not executable here, so the build did not complete. (failed)
• Attempted cd scripts/cn1playground && bash ./mvnw -pl common -DskipTests package, but the Maven wrapper failed to download dependencies due to network/proxy restrictions in this environment. (failed)

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Codex Task

[github-actions]

Cloudflare Preview

• URL: https://pr-4699-website-preview.codenameone.pages.dev
• Branch: pr-4699-website-preview