feat(events): workflow-proposal event model

ProposedWorkflow + WorkflowProposedEvent(sessionId, proposalId, prompt,
candidates, originalRequest), registered in the polymorphic eventModule.
Records the router's triage suggestion of candidate workflows as a
non-authoritative fact the operator acts on.

core/events/src/main/kotlin/com/correx/core/events/events/WorkflowProposalEvents.kt

@@ -0,0 +1,32 @@
+package com.correx.core.events.events
+
+import com.correx.core.events.types.SessionId
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * One workflow the router suggests for an operator request it cannot answer or steer directly, with
+ * a short [reason]. [workflowId] is one of the registered workflow ids the router was shown.
+ */
+@Serializable
+data class ProposedWorkflow(
+    val workflowId: String,
+    val reason: String = "",
+)
+
+/**
+ * The router triaged an operator request to one or more candidate workflows (option (a) of its
+ * triage path). Recorded as a fact (invariants #1/#9): the client renders [candidates] as a choice
+ * panel and, on selection, launches the chosen workflow seeded with [originalRequest] — or, via the
+ * panel's manual-answer slot, continues the conversation. Non-authoritative: nothing runs until the
+ * operator picks, so this never starts a workflow on its own.
+ */
+@Serializable
+@SerialName("WorkflowProposed")
+data class WorkflowProposedEvent(
+    val sessionId: SessionId,
+    val proposalId: String,
+    val prompt: String,
+    val candidates: List<ProposedWorkflow>,
+    val originalRequest: String = "",
+) : EventPayload

core/events/src/main/kotlin/com/correx/core/events/serialization/Serialization.kt

@@ -56,6 +56,7 @@ import com.correx.core.events.events.ToolInvokedEvent
 import com.correx.core.events.events.TransitionExecutedEvent
 import com.correx.core.events.events.WorkflowCompletedEvent
 import com.correx.core.events.events.WorkflowFailedEvent
+import com.correx.core.events.events.WorkflowProposedEvent
 import com.correx.core.events.events.WorkflowStartedEvent
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.modules.SerializersModule
@@ -121,6 +122,7 @@ val eventModule = SerializersModule {
         subclass(HealthRestoredEvent::class)
         subclass(ClarificationRequestedEvent::class)
         subclass(ClarificationAnsweredEvent::class)
+        subclass(WorkflowProposedEvent::class)
     }
 }