discover_plugin_cli_commands() now reads memory.provider from config.yaml
and only loads CLI registration for the active provider. If no memory
provider is set, no plugin CLI commands appear in the CLI.
Only one memory provider can be active at a time — at most one set of
plugin CLI commands is registered. Users who haven't configured honcho
(or any memory provider) won't see 'hermes honcho' in their help output.
Adds test for inactive provider returning empty results.
0f813c422c