feat(confidence-engine): use server investigation persistence

lib/storage/restart-investigation.js

@@ -0,0 +1,13 @@
+export function restartSnapshot(snapshot, now = new Date().toISOString()) {
+  return {
+    ...snapshot,
+    situationGraph: null,
+    selectedQuestion: null,
+    summary: null,
+    focusedContributions: [],
+    findings: [],
+    investigationReport: null,
+    investigationRevision: 0,
+    updatedAt: now,
+  };
+}