test: cover issue 1087

[brentthomas248]

Closes #1087

Summary:

• Add focused happy-path unit coverage for LoggerService warn/debug/verbose methods.
• Add structured logging happy-path coverage for supported log levels and request-context metadata.
• Keep the change scoped to backend common logging tests.

Tests:

• npm test --prefix backend -- logger.service.spec.ts
• git diff --check

Notes:

• npx --no-install eslint src/common/services/logger.service.spec.ts reports existing file-level Prettier and @typescript-eslint/no-unsafe-assignment issues outside the new test block.