test: resolve issues #1837, #1840, #1839, #1838 with integration test…

[Favourof]

Description

This PR resolves four related testing, resilience, and security issues across the codebase:

• [Testing] Write integration tests for MTN payout confirmation routines #1837: Added integration test suite for MTN payout confirmation, status polling, batch payout routines, database reconciliation, and HMAC SHA-256 callback verification.
• [Testing] Create unit tests for transaction CSV exporter utility #1838: Extracted modular CSV exporter utility (csvExporter.ts) and created unit tests covering escaping, filter parsing, parameterized query generation, and stream transforms.
• [Testing] Set up security scanning tools in test pipeline #1839: Configured CI security scanning workflow (Dependency Audit, CodeQL, Secret Scanning, Trivy) and automated security validation tests.
• [Testing] Verify error propagation and recovery loops during network failures #1840: Added chaos and error propagation tests verifying transient network error detection, exponential backoff retries, and circuit breaker recovery loops.

Changes

• src/tests/integration/mtnPayoutConfirmation.test.ts
• src/utils/csvExporter.ts & src/utils/__tests__/csvExporter.test.ts
• src/routes/export.ts
• .github/workflows/security-scan.yml & scripts/security-scan.ts
• src/tests/security/securityPipeline.test.ts
• src/tests/chaos/networkFailureRecovery.test.ts
• package.json

Closes #1837, Closes #1838, Closes #1839, Closes #1840

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