feat(ui): add offline UI

[pwltr]

Description

• add UI for offline state in various flows
• add connection lost/restored toast
• improve app status logic for offline state
• polish and refactor animated loading UI

Screenshot / Video

iPhone 17:

Simulator.Screen.Recording.-.iPhone.17.-.2026-04-22.at.18.23.36.mov

iPhone SE:

Simulator.Screen.Recording.-.iPhone.SE.3rd.generation.-.2026-04-22.at.18.25.27.mov

QA Notes

To test use the app while offline / in airplane mode

[piotr-iohk]

I tested this branch offline and found two things:

1. Question about expected scope: should the connection issue UI handle only OS-level offline state, or also request-level connectivity failures? With Network Link Conditioner set to 100% loss, NWPathMonitor still seems to report the path as connected, so I get raw backend error toasts instead of the connection issue screen.

Screen.Recording.2026-05-12.at.09.05.16.mov

2. When I fully disconnect Wi-Fi, the connection issue screen appears as expected. But after reconnecting Wi-Fi, the app does not recover until I restart it. The offline UI stays stuck even though connectivity is back.

Screen.Recording.2026-05-12.at.09.02.30.mov

Full log from testing:
bitkit_logs_2026-05-12_07-08-14.zip