Each provider now declares its config surface in config_schema.py inside
its own plugin dir (plugins/memory/<name>/), loaded by file path like the
plugins themselves so plugin __init__ imports never reach the web server.
hermes_cli/memory_providers.py is gone; the shared field primitives and
loader live in plugins/memory/config_schema.py, and the schema tests move
to tests/plugins/memory/ alongside the other per-plugin suites.
