🐛 Fix sync ordering for kubeconfig provider

[zachaller]

Fix race condition and resource leak in kubeconfig provider

Summary

This PR fixes two issues in the kubeconfig provider's cluster engagement flow:

1. Race condition: Ensures clusters are fully ready before being exposed via the provider
2. Resource leak: Properly cleans up context when engagement fails

Changes

Call Engage before waiting for cache sync

• The cluster must be engaged with the manager before waiting for cache sync
• This allows controllers and watches to be set up, which populate the cache
• Waiting for sync before engaging would result in an empty cache

Ordering rationale

1. Start cluster (goroutine)
2. Engage with manager → sets up controllers/watches
3. Wait for cache sync → ensures cache is populated
4. Store in map → makes cluster accessible to callers
5. Log success → confirms cluster is fully operational

This ordering prevents external code from accessing an unready cluster and avoids context leaks on failure.

[k8s-ci-robot]

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