The gRPC client was not sending the authorization header, causing
"missing authorization header" errors even when a token was configured.
Also fix config test to isolate from real ~/.config/mcrctl.toml.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Loads defaults from ~/.config/mcrctl.toml (or XDG_CONFIG_HOME).
Resolution order: flag > env (MCR_TOKEN) > config file.
Adds --config flag to specify an explicit path.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
