fix: add activity refresh error banner

[Binali223]

Overview

This PR adds a non-blocking activity refresh error banner. When a refresh attempt fails but cached or previous activity data is still available, the history screen keeps showing the existing transactions and displays a clear banner with a retry action. Full-screen error handling is preserved for the case where no activity data exists at all.

Related Issue

Closes #

Changes

🔄 Activity State Handling

• [MODIFY] src/store/walletStore.ts

  • Keeps existing transactions when a refresh error occurs; only clears data on a successful load or initial full-screen error.
  • Adds refreshError, isRefreshing, and retryRefresh to the activity state.
  • Exposes a retry action so the banner can trigger another refresh without losing visible data.

• [MODIFY] src/features/transactions/types.ts

  • Adds refresh status and error state to the activity store types.

• [MODIFY] src/features/transactions/helpers.ts

  • Distinguishes initial load failures from refresh failures so the UI can choose the correct presentation.

🧩 UI Components

• [MODIFY] app/(tabs)/history.tsx

  • Renders NetworkStateBanner when a refresh error exists and activity data is already available.
  • Keeps full-screen ErrorState only when no activity data is available.

• [MODIFY] src/components/ErrorState.tsx

  • Restricts full-screen error usage to initial load / no-data failures.

• [MODIFY] src/components/NetworkStateBanner.tsx

  • Adds a non-blocking refresh failure banner with a clear, non-sensitive message and a Retry button.

Verification Results

Manual verification:
✅ Existing activity data remains visible after simulated refresh failure
✅ Refresh failure banner is shown without replacing content
✅ Retry refresh re-runs activity load and updates data
✅ Full-screen error is still used when no activity data is available
✅ Banner message is generic and non-sensitive for Testnet/network failures

Acceptance Criteria	Status
Existing activity data remains visible after refresh failure	✅ Cached transactions are preserved and rendered
Refresh failure banner is shown	✅ Non-blocking banner appears with clear message
User can retry refresh	✅ Retry button triggers retryRefresh on wallet store
Full-screen error is still used when no activity data is available	✅ Initial load failure still uses full-screen error
Error message is clear and non-sensitive	✅ Generic network/Testnet message, no sensitive details

Closes #100