sunbeam apply [namespace] builds the full kustomize overlay (preserving
all image substitutions and patches) then filters the output to only
resources in the given namespace before applying. Cleanup and ConfigMap
restart detection are also scoped to the target namespace.
- manifests.py: _filter_by_namespace(), scoped pre_apply_cleanup()
- cli.py: namespace positional arg for apply; meet added to build choices
- tests: 17 new tests covering filter logic and CLI dispatch