feat: surface risk rationale to operator in approval prompt

Carry the full RiskSummary (level, signals, rationale) inline on
ApprovalRequestedEvent instead of discarding it after assessment. The two
server-side DTO builders (live ApprovalCoordinator path and replay
DomainEventMapper path) now render real risk level, recommended action,
signal factors, and the [code] rationale lines into the approval WebSocket
message, with a consistent enum-name fallback when no assessment ran (tool
path). RiskSummary/RiskSignal made @Serializable for event embedding;
shared RiskSummary.toDto() lives next to RiskSummaryDto.

core/approvals/src/main/kotlin/com/correx/core/approvals/model/DomainApprovalRequest.kt

@@ -2,6 +2,7 @@ package com.correx.core.approvals.model
 
 import com.correx.core.approvals.Tier
 import com.correx.core.approvals.UserSteering
+import com.correx.core.events.risk.RiskSummary
 import com.correx.core.events.types.ApprovalRequestId
 import com.correx.core.events.types.CausationId
 import com.correx.core.events.types.CorrelationId
@@ -16,6 +17,7 @@ data class DomainApprovalRequest(
     val tier: Tier,
     val validationReportId: ValidationReportId,
     val riskSummaryId: RiskSummaryId?,
+    val riskSummary: RiskSummary? = null,
     val timestamp: Instant,
     val causationId: CausationId? = null,
     val correlationId: CorrelationId? = null,