test: add security audit repo coverage and horizon diagnostics

[Ukorstack]

Summary

Closes #1078. Add a dedicated test suite for src/security/audit.ts and harden the health route diagnostics.

• src/security/audit.test.ts (new, 63 tests): focused behavior coverage for InMemorySecurityAuditRepository (initial state, record/retrieve, ordering, limits, security-violation filtering, clear/re-populate transitions, instance isolation, capacity-eviction boundary, invalid inputs), DatabaseSecurityAuditRepository (SQL + parameter contract via mocked pool, row mapping, empty results, error propagation), SECURITY_AUDIT_EVENTS_SCHEMA DDL assertions, createSecurityAuditRepository env selection, and the module's hash-chain/scheduler re-export surface. All fixtures are deterministic — fixed IDs and timestamps, no wall-clock reads or sleeps.
• src/routes/health.ts: report the last attempted Horizon endpoint in failure details.url so operators can identify a failing endpoint without exposing error internals; also removes an unused import and an implicit-any that tripped eslint.

Public contract

No production behavior changed beyond the additive details.url diagnostic field on Horizon health failures. Existing exports, SQL shapes, and schemas are asserted as-is.

Validation

Check	Result
Focused suite npx jest src/security/audit.test.ts	63 passed
Surrounding suite npx jest src/security/	10 suites, 151 tests passed
src/routes/health.test.ts	74 passed
Lint npx eslint on changed files	clean (2 pre-existing errors in health.ts fixed in this PR)
Type check npx tsc --noEmit	no errors in changed files (250 pre-existing errors in unrelated src/vaults/* files)

Security notes

• Diagnostic url field exposes only the configured Horizon endpoint URL (public configuration); no error internals or secrets are leaked.
• Audit tests verify parameterized SQL usage, fail-safe empty results for unknown lookups, and unchanged propagation of pool errors.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff noreply@codebuff.com

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[Ukorstack]

kindly review please!