[test-recorder] Cleanup: unexported test seams and single-use ui/steps module

### Problem
Minor dead surface and single-use structure:

- Exports with no non-test external import: `parseChangeSummary` (`src/agent/refactor.ts:109`), `AGENT_CLI_ADAPTERS` (`src/checks/agentCli.ts:13`), `displayWidth` (`src/ui/logger.ts:40`), `buildTestPlan` (`src/commands/plan.ts:42`), `filterWorkflows` (`src/commands/list.ts:5`).
- `src/ui/steps.ts:1-7` is a seven-line module wrapping `header` with step metadata, used only by `record`.

### Suggested fix
Make helpers private (test through command behavior or colocated tests) and fold `stepHeader` into `ui/logger.ts`.

_Line references are against branch `cb/comfy-test-usability` (PR #15837); adjust after merge._