fix(sessions): terminalize session on workflow completion

DefaultSessionReducer skipped WorkflowCompletedEvent to avoid terminalizing on freestyle planning's mid-session completion, but that left execution/normal completions stuck ACTIVE forever — headless watchers and approval loops never saw a terminal state. Add workflowId to WorkflowCompletedEvent (defaulted for replay compat), pass graph.id at all completeWorkflow sites, and terminalize to COMPLETED unless it's the freestyle_planning handoff. Correct stale tests that pinned the ACTIVE-forever behavior.

testing/replay/src/test/kotlin/TransitionReplayIntegrationTest.kt

@@ -80,7 +80,7 @@ class TransitionReplayIntegrationTest {
         val state = replayer.rebuild(sessionId)
 
         assertEquals(
-            SessionStatus.ACTIVE,
+            SessionStatus.COMPLETED,
             state.status
         )
     }