Add unit tests for HarnessDeployer

[jariy17]

Problem

src/cli/operations/deploy/imperative/deployers/harness-deployer.ts (370 lines) has zero unit tests. It contains retry logic, polling, role resolution, create/update/delete branching, and error handling — all untested.

harness-mapper.test.ts covers the mapping layer but not the deployer orchestration.

What to test

• createWithRetry — IAM role propagation retry behavior, max retries exhausted
• waitForReady — polling success, timeout, FAILED terminal state
• deploy() — create vs update branching based on existing state, partial failure handling, deletion of removed harnesses
• teardown — reverse-order cleanup, error propagation
• resolveRoleArn — CDK output key matching (both old and new construct layouts)

Context

Found during review of #1341.