v0.1.1-alpha.1

Don't auto-create contexts on read; seed namespace on login (#14)

get-contexts, use-context, and the --context override now use a
read-only config load and never create or seed a context:

  - get-contexts on an empty config prints just the header
  - use-context errors on an unknown/empty config
  - --context fails if the named context does not exist

The current-context path still seeds a default-server context on first
use, so resource commands (agents/tools) work out of the box.

login now seeds a blank context namespace with the first namespace the
server reports (best-effort; existing namespaces are preserved).

When a context has no namespace, the error now directs the user to run
`rossoctl login` rather than `config set-context --namespace`.

Signed-off-by: Ed Snible <snible@us.ibm.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>