fix: complete P4 audit findings — steering wiring, generation config

P4-1: Wire steering to actually work (advisory-only):
  - RouterFacade emits SteeringNoteAddedEvent via event store in STEERING mode
  - SessionOrchestrator reads steering notes from event store and includes them
    as ContextEntry objects (sourceType=steeringNote) in stage context packs
  - Delete dead SteeringNote data class; single vocabulary = SteeringNoteAddedEvent
  - Add optional validateSteering callback to DefaultRouterFacade for future
    ValidationPipeline wiring (avoids cross-core dependency)
  - Update RouterFacadeTest to assert event emission

P4-2: Router FACE — move hardcoded generation config:
  - Add GenerationConfig field to RouterConfig with same defaults
  - RouterFacade uses config.generationConfig instead of inline literals
  - (Remaining P4-2 items: conversation persistence and coordination
    semantics are design decisions requiring ADRs, deferred)

testing/deterministic/src/test/kotlin/RouterFacadeTest.kt

@@ -81,17 +81,18 @@ class RouterFacadeTest {
     }
 
     @Test
-    fun `STEERING mode does not append events to store`(): Unit = runBlocking {
-        // SteeringNoteAddedEvent emission is deferred to P4-1 (see P0-6).
-        // The steeringEmitted flag still informs the TUI that steering mode was used.
+    fun `STEERING mode appends SteeringNoteAddedEvent to store`(): Unit = runBlocking {
         val mockStore = mockEventStore()
         val facade = facadeWithMocks(eventStore = mockStore, chatMode = ChatMode.STEERING)
         facade.onUserInput(sessionId = SessionId("session-xyz"), input = "steer this way")
-        assertTrue(mockStore.appendedEvents.isEmpty())
+        assertEquals(1, mockStore.appendedEvents.size)
+        val payload = mockStore.appendedEvents.single().payload
+        assertTrue(payload is com.correx.core.events.events.SteeringNoteAddedEvent)
+        assertEquals("inference response", (payload as com.correx.core.events.events.SteeringNoteAddedEvent).content)
     }
 
     @Test
-    fun `STEERING mode does not append events regardless of state stageId`(): Unit = runBlocking {
+    fun `STEERING mode appends SteeringNoteAddedEvent with current stageId`(): Unit = runBlocking {
         val mockStore = mockEventStore()
         val stageId = StageId("stage-A")
         val facade = DefaultRouterFacade(
@@ -106,12 +107,15 @@ class RouterFacadeTest {
             routerContextBuilder = object : RouterContextBuilder {
                 override suspend fun build(state: RouterState, budget: TokenBudget): ContextPack = emptyContextPack()
             },
-            inferenceRouter = mockInferenceRouter("response"),
+            inferenceRouter = mockInferenceRouter("steering response"),
             eventStore = mockStore,
             config = RouterConfig(tokenBudget = TokenBudget(limit = 5000)),
         )
         facade.onUserInput(sessionId = SessionId("test-session"), input = "Hello!", mode = ChatMode.STEERING)
-        assertTrue(mockStore.appendedEvents.isEmpty())
+        assertEquals(1, mockStore.appendedEvents.size)
+        val payload = mockStore.appendedEvents.single().payload
+        assertTrue(payload is com.correx.core.events.events.SteeringNoteAddedEvent)
+        assertEquals("steering response", (payload as com.correx.core.events.events.SteeringNoteAddedEvent).content)
     }
 
     // --------------------------------------------------------------------------
@@ -449,8 +453,7 @@ class RouterFacadeTest {
         assertNotNull(response)
         assertEquals("inference response", response.content)
         assertTrue(response.steeringEmitted)
-        // Steering events are deferred to P4-1; no events appended yet.
-        assertTrue(mockStore.appendedEvents.isEmpty())
+        assertEquals(1, mockStore.appendedEvents.size)
     }
 
     // --------------------------------------------------------------------------