fix(stellar): report a failed balance lookup instead of an empty balance

[Shindy-Ship]

Overview

This PR separates a failed balance lookup from an empty balance in the Stellar balance path. Previously StellarService.checkBalance swallowed errors from this.server.loadAccount(publicKey) and returned [], which handleBalance rendered as a balance.success message with an empty string — telling users they had nothing when Horizon was actually unreachable. Now a failed lookup is surfaced to the caller and reported as an unavailable balance, while a genuinely unfunded account still renders as an empty balance.

Related Issue

Changes

🔍 Balance Lookup Distinguishes Failure from Empty

• [MODIFY] src/services/stellar.service.ts

  • checkBalance no longer returns [] on a failed loadAccount call; the failure is propagated to the caller instead of being masked as an empty balance.
  • The not-found case is kept distinct, matching how the history path already inspects the status code and reports an unfunded wallet separately.

• [MODIFY] src/services/message-processor.service.ts

  • handleBalance now handles the failed-lookup outcome separately from an empty result, so an outage produces an unavailable-balance message rather than a zero balance.

• [MODIFY] src/locales/en.json

  • Added the user-facing string for an unavailable balance, distinct from the existing empty-balance message.

🧪 Tests

• [MODIFY] src/__tests__/stellar.service.test.ts

  • Covers a failed lookup being surfaced rather than returned as an empty list.

• [MODIFY] src/__tests__/message-processor.service.test.ts

  • Covers the failed-lookup path rendering an unavailable-balance message and the no-funds path still rendering an empty balance.

Verification Results

npm test
✅ passes locally

Acceptance Criteria	Status
A failed lookup does not render as a zero balance	✅ Failure is surfaced and reported as unavailable
An account with no funds still renders as an empty balance, not an error	✅ Not-found case kept distinct from failure
The user-facing message differs between the two cases	✅ Separate unavailable-balance string added in en.json
A test covers each	✅ Added to stellar.service.test.ts and message-processor.service.test.ts
npm test passes locally	✅ Passes

Closes #250

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