feat: add self-contained v1beta1 platform runtime

[sphr2k]

Summary

• render v1beta1 platforms from a compact local CUE runtime instead of copying the generated CUE SDK into every fresh platform
• add a generic platform-root Kustomize base task with contained paths and optional LoadRestrictionsNone
• cover local Helm values, raw Kubernetes resources, Kustomize bases outside component roots, and no-vendor platform initialization

Verification

• make test
• go test ./api/... ./cmd/... ./internal/... -count=1
• go vet ./...

The full CUE SDK remains available only to internal compatibility fixtures that intentionally import the legacy author packages; holos init platform v1beta1 itself does not emit it.