feat: add archive manifest sample

Author: AvaPrime

examples/conversation-export/packaged/export-manifest.sample.json

@@ -0,0 +1,14 @@
+{
+  "export_id": "export",
+  "record_counts": {
+    "conversations": 1,
+    "messages": 2,
+    "pairs": 1
+  },
+  "generated_files": [
+    "conversation-records.json",
+    "message-records.json",
+    "message-pairs.json"
+  ],
+  "packaging_mode": "directory"
+}