docs: consolidate design documentation and standardize crate English

crates/feature-storage/README.md

@@ -1,28 +1,11 @@
 # feature-storage
 
-Neutral Host-owned SQLite lifecycle manager for trusted Features. Owns placement,
-WAL/connection settings, transaction serialization, migrations, snapshots,
-restore/delete fencing, and shutdown. Features receive a managed
-`FeatureDatabase` after registration. Worker/model input never selects a database
-path or receives SQL access.
+Manages the SQLite lifecycle for Features within a trusted Host.
+Does not own Feature domain schemas or authentication, or provide SQL access to Workers or models.
 
-Use `FeatureStorage::new(trusted_root)`, `register(FeatureRegistration)`, and
-`scope(host_issued_scope_id).open(&registration)`. `ScopedFeatureStorage` and
-`FeatureDatabase::scope_id()` are neutral storage isolation APIs: a local Host's
-persisted random scope does not create a Workspace record or imply Backend
-membership. Existing placement `<root>/<scope>/features/<feature>.sqlite` and
-snapshot `workspace=` keys remain unchanged for physical compatibility.
+## Main entry points
 
-`WorkspaceFeatureStorage`, `workspace()`, `workspace_id()`, and
-`for_server_database()` are Backend compatibility aliases/helpers. They do not
-introduce a Server dependency. The Host is responsible for state-root privacy,
-symlink/path validation, and external execution leases before constructing this
-trusted manager.
-
-`configure_connection(&rusqlite::Connection)` is reusable by other Host stores
-(such as JobStore). It sets the five-second busy timeout, foreign keys ON, WAL,
-and synchronous FULL before migrations/transactions. The Feature manager uses
-this same helper; WAL lock-contention retries stay within the busy timeout.
-
-Dependencies: `rusqlite` (existing workspace backup support), `thiserror`, `uuid`;
-tests use `tempfile`.
+- [`FeatureStorage`], [`ScopedFeatureStorage`]: registration, scope isolation, storage, and shutdown
+- [`FeatureDatabase`]: connections and transactions
+- [`FeatureMigration`]: Feature-owned schema changes
+- [`configure_connection`]: shared SQLite connection policy