[S6] Write tests for PR validation and scheduled reconciliation

[krakenhavoc]

Description

Test suites for PR validation flow and cron-based reconciliation.

PR Validation Tests

• PR with valid config change → passing check
• PR with invalid config → failing check with details
• PR without config change → no check run
• PR with both root and .github/ config → warning in check

Scheduled Reconciliation Tests

• Cron fires and processes all active repos
• Rate limit backoff is triggered when remaining is low
• Staggered job timing
• Inactive installations/repos are skipped

Acceptance Criteria

• All test scenarios covered
• Rate limit behavior tested
• Tests are deterministic and fast