fix: wait for node Ready before helm install, increase timeout to 15m

'client rate limiter Wait: context deadline exceeded' happens when the
API server is still warming up on a fresh cluster and queued requests
exhaust the context before getting a rate-limiter slot.

Wait for all nodes to be Ready before any Helm operation so the API
server is fully available. Increase --timeout from 10m to 15m to give
more headroom on slow cluster starts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>