Add blockchain transaction monitoring and alerting for failed/ stalled transactions

[Smartdevs17]

Description

Blockchain transactions can fail or get stuck without notification. Implement monitoring that tracks transaction status and alerts on anomalies.

Acceptance Criteria

• Transaction status tracking from submission to finality
• Stuck transaction detection (no status change within timeout)
• Failed transaction analysis with error categorization
• Automated retry for transient failures
• Alerting via email/Push/webhook on critical failures
• Transaction health dashboard

Technical Scope

• backend/src/services/stellar.ts
• backend/src/services/failure-analysis.ts
• backend/src/routes/
• Edge: chain reorganization handling, mempool eviction detection