0023 Namespace manifests in ns/ subdirectory

Context and Problem Statement

Base-apps categories group resources by namespace (e.g. backup/, secrets/). Each category includes a namespace manifest and one or more apps. Placing namespace.yaml at the category root forces consumers to either take the entire category or manually exclude the namespace when picking individual apps.

Decision Outcome

Place namespace manifests in an ns/ subdirectory with its own kustomization.yaml. The category-level kustomization references ./ns alongside individual apps.

backup/
  kustomization.yaml    # includes ./ns, ./volsync
  ns/
    kustomization.yaml  # includes namespace.yaml
    namespace.yaml
  volsync/
    ...

This lets consumers pick ns/ + specific apps, or include the whole category. Consistent with the existing pattern in gitlab/ and secrets/.