[S7] Write end-to-end integration test

[krakenhavoc]

Description

Full flow integration test covering the complete lifecycle.

Test Flow

1. Simulate App installation webhook → installation record created
2. Simulate push with .krakenkey.yml → config parsed, reconciliation triggered
3. Reconciler requests cert via mocked ACME service → cert issued
4. Deploy to mocked GitHub Secrets API → secret set
5. Check run posted to mocked GitHub API → verified
6. Simulate second push with no config change → reconciliation skipped (SHA match)
7. Simulate push with cert approaching expiry → renewal triggered
8. Simulate PR with invalid config → failing check run

Acceptance Criteria

• Full lifecycle test passes
• All integration points verified
• Test runs in CI
• Test is deterministic (no flaky timing)