test(cli): import inquirerer test utils directly from @inquirerer/test

[pyramation]

Summary

The packages/cli/test-utils/index.ts barrel was a pure passthrough re-export of @inquirerer/test, which made it look like there was a custom test harness when there wasn't. This makes cli.test.ts import from @inquirerer/test directly so the source is obvious, and trims test-utils/index.ts down to the genuinely local fixture helpers.

- import { KEY_SEQUENCES, setupTests, TestEnvironment } from '../test-utils';
+ import { KEY_SEQUENCES, setupTests, TestEnvironment } from '@inquirerer/test';

No behavioural change — the symbols are identical (the local barrel was just export { ... } from '@inquirerer/test'). test-utils/fixtures.ts stays put because it's a genuinely local wrapper around createTestFixture.

Review & Testing Checklist for Human

• pnpm --filter @constructive-io/cli test still passes locally (with @constructive-io/graphql-codegen built — both cli.test.ts and codegen.test.ts should be green).
• No other packages/cli/test-utils imports got broken — confirmed via grep, only cli.test.ts referenced this path.

Notes

Companion PR: constructive-io/dev-utils#79 adds a runCli subprocess helper to @inquirerer/test and a Testing section to inquirerer's main README pointing at the package. This PR is independent of that one (it just uses the existing in-process setupTests API), but they're part of the same "make CLI testing easy and discoverable" thread.

A separate downstream PR will follow in constructive-io/agentic-db to swap the hand-rolled runCli in cli-e2e-tests for the new shared helper once dev-utils#79 lands.

Link to Devin session: https://app.devin.ai/sessions/81001448b7c54b8099437f706d44a30d
Requested by: @pyramation

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