[Feature] Improve offline detection and graceful degradation for network errors

[kelly-musk]

Problem

components/error/OfflineBoundary.tsx exists but its integration in the app layout is unclear. During a network disruption, API calls fail silently or show generic error states.

For users in markets with intermittent connectivity (a primary target for Aframp), graceful offline handling is critical.

Fix

1. Ensure <OfflineBoundary /> wraps all data-dependent pages
2. Add service worker caching for exchange rates (stale-while-revalidate)
3. Show a non-blocking 'You are offline' banner with last-known data timestamp
4. Queue non-urgent actions for retry on reconnect

Impact

Medium UX — important for African markets with variable connectivity.

[coderolisa]

@coderolisa has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer let me work on this
please assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @coderolisa to this issue.

[1sraeliteX]

@1sraeliteX has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer, I would like to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @1sraeliteX to this issue.