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)

core/kernel/src/main/kotlin/com/correx/core/kernel/orchestration/SessionOrchestrator.kt

@@ -35,6 +35,7 @@ import com.correx.core.events.events.NewEvent
 import com.correx.core.events.events.OrchestrationPausedEvent
 import com.correx.core.events.events.OrchestrationResumedEvent
 import com.correx.core.events.events.RiskAssessedEvent
+import com.correx.core.events.events.SteeringNoteAddedEvent
 import com.correx.core.events.events.ToolExecutionRejectedEvent
 import com.correx.core.events.events.ToolInvocationRequestedEvent
 import com.correx.core.events.events.ToolRequest
@@ -237,12 +238,13 @@ abstract class SessionOrchestrator(
             ?: ResponseFormat.Text
 
         val schemaEntries = buildSchemaEntries(responseFormat, stageId)
+        val steeringEntries = buildSteeringNoteEntries(sessionId)
 
         val contextPack = contextPackBuilder.build(
             id = ContextPackId(UUID.randomUUID().toString()),
             sessionId = sessionId,
             stageId = stageId,
-            entries = systemPrompt + schemaEntries + promptEntries,
+            entries = systemPrompt + schemaEntries + promptEntries + steeringEntries,
             budget = TokenBudget(limit = stageConfig.tokenBudget),
         )
 
@@ -544,6 +546,23 @@ abstract class SessionOrchestrator(
         )
     }
 
+    private suspend fun buildSteeringNoteEntries(sessionId: SessionId): List<ContextEntry> {
+        val events = eventStore.read(sessionId)
+        return events.mapNotNull { event ->
+            (event.payload as? SteeringNoteAddedEvent)?.let { steering ->
+                ContextEntry(
+                    id = ContextEntryId(UUID.randomUUID().toString()),
+                    layer = ContextLayer.L2,
+                    content = steering.content,
+                    sourceType = "steeringNote",
+                    sourceId = steering.stageId?.value ?: sessionId.value,
+                    tokenEstimate = estimateTokens(steering.content),
+                    role = EntryRole.SYSTEM,
+                )
+            }
+        }
+    }
+
     private suspend fun emitToolArtifacts(
         sessionId: SessionId,
         stageId: StageId,