fix(mobile): Retry account loading without losing navigation#6

What Changed

When T3 Account is still loading on mobile, the Settings row stays tappable and opens a "Checking T3 Account" screen with a spinner and a Retry button. Retry reloads the account provider without clearing app data.

The app keeps its navigation position across that reload, so Retry returns to the same screen rather than the start of the app. Account sign-in transitions that are already in progress survive the reload, and reloading no longer drops the active relay session. Signing out still goes through the normal sign-out path.

Why

If account loading stalled, the T3 Account row showed "Checking" and was disabled, and the account screen rendered nothing, so the only way out was to kill the app or clear its data. Navigation state is kept in memory only, so a cold start still opens at the default screen.

UI Changes

Adds the "Checking T3 Account" screen with a Retry button, and the T3 Account row is no longer disabled while loading. No screenshots are attached.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes