Add health check gatekeeper for hub integration tests

[shanevcantwell]

Problem

Hub integration tests in extensions/cli/src/hubLoader.test.ts can fail spuriously when the Hub API experiences 5xx errors or outages. This creates noise in CI and makes it harder to identify real test failures.

Suggested Solution

Add a health check helper that runs before integration tests and gracefully skips them if the Hub API is unavailable:

describe("Real Hub Integration Tests", () => {
  let hubAvailable = false;
  
  beforeAll(async () => {
    hubAvailable = await isHubAvailable();
    if (!hubAvailable) {
      console.warn("Hub API unavailable - skipping integration tests");
    }
  });

  async function isHubAvailable(): Promise<boolean> {
    try {
      const response = await fetch(`${env.apiBase}health`, {
        signal: AbortSignal.timeout(5000),
      });
      return response.ok;
    } catch {
      return false;
    }
  }

  it("should load rule from real hub", async () => {
    if (!hubAvailable) return;
    // actual test
  });
});

Benefits

• Prevents spurious CI failures from external service outages
• Makes tests more reliable without changing functionality
• Standard practice for integration testing
• Graceful degradation (logs warning, doesn't fail build)

Context

Discovered while working on PR #9314 - the hub integration tests failed with 5xx errors during an apparent service outage, blocking an unrelated PR.

[continue]

Related Issues

• Fix the CI pipeline tests once and for all to be able to actually make use of them #8355 - Fix the CI pipeline tests once and for all to be able to actually make use of them (broader test stability issue that this addresses for hub integration tests)