feat: add API reported and health server

[krakenhavoc]

This pull request introduces two new internal packages, health and reporter, which provide HTTP health/readiness endpoints and API communication logic, respectively. Both packages are well-covered with unit tests to ensure correct behavior and error handling.

Health endpoint implementation and testing:

• Added a new health package with a Server struct that exposes /healthz and /readyz endpoints, tracks probe status, readiness, and scan times, and provides thread-safe updates. (internal/health/health.go)
• Added comprehensive tests for the health package, covering endpoint responses, readiness state, scan time updates, server start/shutdown, and content type validation. (internal/health/health_test.go)

Reporter (API client) implementation and testing:

• Introduced a new reporter package that encapsulates API interactions, including registering the probe, reporting scan results, fetching hosted config, handling authentication, rate limiting, retries, and error formatting. (internal/reporter/reporter.go)
• Added thorough tests for the reporter package, covering successful registration and reporting, error handling (401, 429, 5xx), retry logic, hosted config retrieval, and User-Agent header correctness. (internal/reporter/reporter_test.go)