feat: refresh usage on network and resume recovery

[GcsSloop]

Summary

• trigger an immediate usage refresh when the app comes back online
• trigger an immediate usage refresh after a long hidden/resume transition
• debounce and coalesce burst refresh triggers, then fan back into the existing account sync flow
• document the design in docs/plans

Verification

• npm --prefix frontend test -- --run src/App.test.tsx
• npm --prefix frontend test -- --run src/features/accounts/AccountsPage.test.tsx
• npm --prefix frontend test
• npm --prefix frontend run build