v0.1.2-alpha.1

Add cortex file-backed backend, context types, and cortex commands (#15)

* Add cortex file-backed backend, context types, and cortex commands

Introduce a Context Type ("k8s"/"cortex") and a rossoctlclient.Rossoctl
interface implemented by both apiclient.Client (HTTP) and the new
cortexclient.FileClient (file-backed). rossoctlclient.NewClient dispatches
on the context type.

Add `cortex` commands (start/stop/status/doctor): start/stop/status
resolve or create a cortex-typed context, and doctor is an offline
environment preflight ported from rossoctlx. `cortex start` registers the
rossoctlx start flags. `config delete-context` is also added.

FileClient derives its config paths (honoring XDG_CONFIG_HOME /
ROSSOCORTEX_CONFIG_DIR), seeds its agents/state files, implements
ListAgents (from the agents.json "agents" map) and CreateAgent (records
agent metadata with a Created timestamp).

Move the config dir and binary install location from $HOME/.rossoctl to
$HOME/.config/rossoctl.

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