feat(branding): refresh Sync360 icons across Android and Desktop

Adopt the new Sync360 logo across the Android and Desktop app experience.

Android:
- Update the Play Store image and launcher icons for every supported screen size.
- Refresh the normal, round, foreground, and monochrome icon variants.
- Keep the selected white icon background across the Android launcher artwork.

Desktop:
- Update the Windows, macOS, Linux, and Desktop-window icons with the new logo.
- Keep the Windows and macOS icon files sharp at both small and large system sizes.
- Refresh the small startup splash with the centered Sync360 logo on a clean white background.

UI:
- Give the shared floating navigation bar a more rounded appearance.

This commit updates the visible branding only. It does not change nearby-device discovery,
sharing, or transfer behavior.

Author: CodePandaaAI