[Feature]: add widget intro and add-widget grid

[piotr-iohk]

Problem or use case

The Widgets entry point and add-widget flow need to match the latest Figma designs for the widget release.

Users should see a one-time Widgets intro when they first open Widgets from the menu. After that intro has been shown once, the Widgets menu item should take users directly to the scrolled wallet state that displays widgets.

The Add Widget action should also be updated to use a bottom sheet with a grid of available widgets, including both small and wide widget sizes.

Proposed solution

Implement the Widgets intro and Add Widget flow adjustments from Figma.

Scope:

• Show the Widgets intro onboarding frame only once, when the user first clicks the Widgets menu item.
• Persist that the Widgets intro has been seen.
• After the intro has been seen, route the Widgets menu item to the scrolled wallet state that displays widgets.
• Update Add Widget to open a bottom sheet.
• Show a grid of all available widgets in the bottom sheet.
• Support both small and wide widget sizes in the Add Widget grid.
• Match spacing, layout, copy, and visual states from the linked Figma frames.

Alternatives considered

n/a

Additional context

Figma:

• https://www.figma.com/design/ltqvnKiejWj0JQiqtDf2JJ/Bitkit-Wallet?node-id=43103-187838&t=1BER01UMnjmhR2w5-0
• https://www.figma.com/design/ltqvnKiejWj0JQiqtDf2JJ/Bitkit-Wallet?node-id=43100-273252&t=1BER01UMnjmhR2w5-0