bug: app update check only gates the home screen

[ovitrif]

The app update check (both critical and non-critical) only evaluates when the user reaches the home screen. It doesn't cover onboarding or other flows, so it can miss showing the update prompt entirely on first launch.

Repro steps

1. Install an older build
2. Restore a wallet
3. Expected: the mandatory update full-screen shows
4. Actual: it doesn't show
5. Force-close the app (also from Android app info screen)
6. Reopen the app — now the mandatory update screen shows

Suggestions

• The update check should also cover the onboarding flow (when no wallet is loaded), scoped at the highest level which includes all screens within the app
• This should apply to the non-critical app update sheet too
• iOS has the same home-screen-only gating for non-critical updates (timed sheets triggered from HomeView.onAppear only). Critical updates on iOS are shown at the top level in AppScene so they're not affected, but the non-critical path has the same limitation.

The old React Native App does this much better, gating the Onboarding flow screens too: