feat(mobile): add protocol status banners

[YfengJ]

Closes #60

Summary

• add a reusable mobile protocol status banner component for wallet disconnects, Stellar network mismatches, and stale sync state
• add protocol status state and a recoverable refresh action to the mobile Zustand store
• surface the banners at the top of the dashboard with reconnect/retry actions
• add a pure status-priority rule helper plus tests, and document the mobile status banner feature

Security / recovery notes

• wallet disconnect recovery routes through the existing logout/reconnect flow instead of inventing a new auth path
• retry refresh is bounded to the existing /health endpoint and does not expose wallet secrets or token data
• banner priority is deterministic so a disconnected wallet is shown before network/sync warnings

Validation

• npm test -- --test-reporter=spec
• npx tsc --noEmit
• git diff --check

[YfengJ]

Thanks for the review and merge. I appreciate it.