Core exposes a unified settings interface through Plugin SDK:
- internal/config/registry.go: thread-safe namespaced KV store
- Register/Get/Set/List/Delete with JSON persistence
- Flush() for explicit save to disk
- SettingsAPI in SDK: plugins call plugin.Settings().Get/Set/List
- Full access: read/write any key (core.*, plugin.<name>.*)
- plugin.Registry.SetConfigRegistry() wires it into SDK plugins
- main.go registers core.* keys at startup, flushes on shutdown
- 7 tests for ConfigRegistry