chore(setup): add setup flag verifier

[ffantl-ld]

Describe the solution you've provided

Fourth layer of the guided setup command: the verifier. Polls the LaunchDarkly API to confirm the newly configured SDK has evaluated a flag, so setup can report success (Verifier, DefaultVerifier). Uses the existing resources.Client.

Related issues

Part of the setup-ld feature. Stacked PR — base is ffantl/setup-ld/3-initializer.

Requirements

• I have added test coverage for new or changed functionality

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Note

Low Risk
New setup-only polling helper using the existing HTTP client; no auth or data-model changes.

Overview
Adds a setup verifier so guided setup can confirm the SDK is live after configuration.

A new Verifier polls GET .../sdk-active via resources.Client until active is true or a configurable timeout (defaults: 5s interval, 120s timeout). It returns a VerifyResult with success, attempt count, and elapsed time. DefaultVerifier wires the standard polling settings.

Unit tests cover immediate success and timeout when the endpoint stays inactive.

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