docs: update documentation of STA

docs/domain-layer.md

@@ -2,8 +2,8 @@
 
 **Feature**: 001-modbus-relay-control
 **Phase**: 2 (Domain Layer - Type-Driven Development)
-**Status**: Complete
-**Last Updated**: 2026-01-04
+**Status**: Complete (US1 MVP also complete)
+**Last Updated**: 2026-05-15
 
 ## Overview
 
@@ -419,13 +419,15 @@ backend/src/domain/
 ├── modbus.rs                  # ModbusAddress type
 └── relay/
     ├── mod.rs                 # Relay module exports
-    ├── controler.rs           # RelayController trait (trait definition)
+    ├── controller.rs          # RelayController trait (trait definition)
     ├── entity.rs              # Relay aggregate
-    └── types/
-        ├── mod.rs             # Type exports
-        ├── relayid.rs         # RelayId newtype
-        ├── relaystate.rs      # RelayState enum
-        └── relaylabel.rs      # RelayLabel newtype
+    ├── types/
+    │   ├── mod.rs             # Type exports
+    │   ├── relayid.rs         # RelayId newtype
+    │   ├── relaystate.rs      # RelayState enum
+    │   └── relaylabel.rs      # RelayLabel newtype
+    └── repository/
+        └── label.rs           # RelayLabelRepository trait
 ```
 
 ## Dependency Graph
@@ -558,16 +560,16 @@ Coverage: 100% for domain layer
 
 ## Next Steps
 
-**Phase 3: Infrastructure Layer** (Tasks T028-T040)
+**Phase 4 (US1 MVP) — Complete** — Users can view all 8 relay states and toggle individual relays on/off via the web UI.
 
-Now that domain types are complete, the infrastructure layer can:
+The infrastructure, application, and presentation layers were built on top of these domain types:
 
-1. Implement `RelayController` trait with real Modbus client
-2. Create `MockRelayController` for testing
-3. Implement `RelayLabelRepository` with SQLite
-4. Use domain types throughout infrastructure code
+1. **Infrastructure** (Phase 3): `ModbusRelayController` (real Modbus TCP client) + `MockRelayController` (testing), `SqliteRelayLabelRepository` for persistence, with factory functions for dependency injection
+2. **Application** (Phase 3): `ToggleRelayUseCase`, `GetAllRelaysUseCase`, `HealthMonitor` service
+3. **Presentation** (Phase 4): `RelayApi` handlers with `RelayDto`, REST endpoints (`GET /api/relays`, `POST /api/relays/{id}/toggle`)
+4. **Frontend** (Phase 4): Vue 3 + TypeScript with `RelayCard`, `RelayGrid`, `useRelayPolling` composable (2s polling)
 
-**Key advantage**: Infrastructure layer can depend on stable, well-tested domain types with strong guarantees.
+**Upcoming phases**: US2 (bulk controls), US3 (health monitoring UI), US4 (relay labeling)
 
 ## References