Updating CnD version

[sidprasad]

Updates the bundled Cope and Drag (Sterling Layout) front-end from 4.0.13 to 4.3.1.

Changes

• Rebuilt Sterling/Cope and Drag JS bundles and vendored assets under forge/sterling/build/.
• Bumped version.json to 4.3.1.
• Refreshed web fonts (.woff/.woff2) and PWA icon/startup-image assets, including new startup images for recent device sizes.
• Migrated the web app manifest from manifest.json / manifest.webapp to manifest.webmanifest and updated index.html references accordingly.

Notes

• This is a front-end build/asset update only; no Forge (Racket) source changes are included.