Fixes#1327 - 'clawdbot message --channel telegram' fails with
'Unknown channel: telegram' because plugins weren't loaded.
The Commander code path (non-route-first) calls ensureConfigReady() in
preAction but doesn't load the plugin registry. Channel plugins like
telegram are registered during plugin loading, so getChannelPlugin()
returns undefined without it.
This adds ensurePluginRegistryLoaded() call for commands that need
channel plugin access: message, channels, directory.