proposal: deployah use / project for sticky context and namespace

[atkrad]

Day to day you must pass -n / --context every time, or trust kubeconfig. That is easy to get wrong across local kind and remote clusters. Environments already know the intended context.

deployah use                 # show current
deployah use staging         # environment -> context (+ ns if set)
deployah use -n payments     # namespace only
deployah use --context kind-deployah

Store sticky state in Deployah (.deployah/active or ~/.config/deployah/active.yaml). Optional --kubeconfig-write if you want kubectl to follow. Flags still win.

--context / --namespace
  -> DPY_* env
  -> deployah active state
  -> platform environment.context
  -> kubeconfig

Does not replace the platform file. deployah use is sugar, not the source of truth for namespace (#9).

Related: #9, #28.