OBS 01EN
[Bug]: Scope the local settings cache by backend, revision, and exposure mode
## Problem `SettingsService` keeps one process-global local settings cache for every registered backend: - `src/api/settings-service/settings-service.api.ts:164-179` stores one `{ redacted, encrypted, timestamp }` object. - `src/api/settings-service/settings-service.api.ts:464-471` serves/writes the redacted slot. - `src/api/settings-service/settings-service.api.ts:493-507` serves/writes the encrypted…