feat(ipc): include fetchSource on attachment-preview responses

request-attachment-preview now forwards preview.fetchSource at the top level
of attachment-preview so the Pear UI can show P2P mesh provenance without
parsing nested preview fields.

Phase 60 / v0.8.25.

Co-authored-by: Cursor <[email protected]>

index.js

@@ -334,7 +334,11 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
   }
   if (t === 'request-attachment-preview') {
     const preview = await platform.readAttachmentPreview(msg.attachmentId)
-    send({ type: 'attachment-preview', preview })
+    send({
+      type: 'attachment-preview',
+      preview,
+      fetchSource: preview?.fetchSource || null
+    })
     return true
   }
   if (t === 'upsert-guild-emoji') {