Add mobile balance refresh state machine

[El-swaggerito]

Description

Difficulty: Expert

Type: Feature

Summary

Add a balance refresh state machine for the mobile wallet.

Current Behaviour

Balance refresh behaviour may not distinguish idle, loading, stale, failed, offline, and refreshed states.

Expected Behaviour

The app should expose clear balance refresh states and safe retry behaviour.

Suggested Implementation

Create state model, hooks, UI states, tests, and docs.

Files or Areas Likely Affected

• src/wallet/
• src/accounts/
• src/screens/
• src/components/
• tests/
• docs/

Acceptance Criteria

• Balance refresh state model is implemented.
• Idle, loading, stale, failed, offline, and refreshed states are represented.
• Retry behaviour is handled.
• UI shows clear state feedback.
• Tests cover major refresh states.
• Docs explain refresh behaviour.

Additional Notes

This improves wallet reliability.