feat: connection issues view

[jvsena42]

Related to #873

Description

This PR adds a reusable connection issues overlay view that appears on top of sheet flows (Send, Receive, Transfer) when the device loses internet connectivity.

1. Adds ConnectionIssuesView composable with phone illustration, dashed rings, and a loading spinner
2. Integrates the overlay into SendSheet, ReceiveSheet, and ForceTransferSheet using AnimatedVisibility
3. Auto-dismisses when connectivity is restored, preserving the underlying flow state

Preview

QA Notes

1. Open the Send Bitcoin sheet, toggle airplane mode on
   • Connection Issues overlay should fade in over the send flow
   • Title should read "Send Bitcoin"
   • Dashed yellow rings and phone illustration should be visible
   • Spinner should be animating at the bottom
2. Re-enable connectivity
   • Overlay should fade out
   • Send flow state should be preserved (no navigation reset)
3. Repeat for Receive Bitcoin sheet
   • Title should read "Receive Bitcoin"
4. Repeat for Force Transfer sheet
   • Title should read "Transfer Funds"
5. Repeat for transfer to spending screen
6. Repeat for transfer to savings screen
7. Verify the overlay does not appear when connectivity is stable