Use Platform Icons for KDEConnect widget

The current icon for the widget is nondescript and looks very similar to the square clipboard.
Using the OS platform logo would look much nicer and the purpose of the widget at a glance.

Android and Apple provide high quality logos to represent their platforms
https://developer.android.com/distribute/marketing-tools/brand-guidelines#android_robot
https://developer.apple.com/design/resources/#technologies

Inspect the KDEConnect widget and its current icon, then review the Android and Apple platform brand resources linked in the issue. Replace the nondescript icon with platform-appropriate artwork so the widget's purpose is clear at a glance, and verify both platform variants render correctly.

Written by the indexing model from the issue text.