The custom-endpoint REST handlers ran bare load_config/save_config, so
every add/activate/delete landed in the process-level default profile
regardless of which profile the desktop settings UI was targeting. A
provider added under a non-default profile silently went to default:
visible only in default-bound sessions, absent everywhere else, and
un-addable to another profile without hand-editing its config.yaml.
Scope all four handlers (list/upsert/activate/delete) to the requested
profile via _config_profile_scope, matching /api/config, and spread the
active profile into the four hermes.ts wrappers alongside their existing
validateCustomEndpoint sibling.
