Refactor PDEWelcome UI and add Sketch card composable

Refactored the PDEWelcome screen for improved structure and readability, including extracting the example preview into a reusable Sketch.card composable. Updated icon usage for RTL support, adjusted layout and padding, and improved the examples list initialization. Also, customized scrollbar style in PDETheme for a more consistent UI appearance.

Author: Stefterv