Add mobile secure storage diagnostics

[El-swaggerito]

Description

Difficulty: Expert

Type: Feature

Summary

Add secure storage diagnostics for wallet-related state.

Current Behaviour

Secure storage failures may be difficult to distinguish from wallet, app, or permission issues.

Expected Behaviour

The app should provide safe diagnostics for secure-store availability and failure states without exposing secrets.

Suggested Implementation

Create diagnostics utilities, redaction, UI support, tests, and docs.

Files or Areas Likely Affected

• src/storage/
• src/wallet/
• src/diagnostics/
• src/screens/
• tests/
• docs/

Acceptance Criteria

• Secure storage diagnostics are implemented.
• Failure states are represented safely.
• Secrets are never exposed.
• Wallet screens can use diagnostics where appropriate.
• Tests cover secure-store failure cases.
• Docs explain diagnostics usage.

Additional Notes

This is sensitive and must avoid leaking wallet data.