revert: restore reply preview logic in NIP-10 adapter

Reverted changes to eventToMessage() that removed reply previews
for root replies. The UI-level hiding of reply interactions on the
root message is sufficient - reply previews can still be shown for
consistency with other messages.

Changes:
- Restored rootEventId parameter (removed underscore prefix)
- Restored full reply detection logic (reply, root, or fallback)
- Reply previews now shown for all replies including root replies

src/lib/chat/adapters/nip-10-adapter.ts

@@ -847,7 +847,7 @@ export class Nip10Adapter extends ChatProtocolAdapter {
   private eventToMessage(
     event: NostrEvent,
     conversationId: string,
-    _rootEventId: string,
+    rootEventId: string,
   ): Message | null {
     // Handle zap receipts (kind 9735)
     if (event.kind === 9735) {
@@ -867,12 +867,14 @@ export class Nip10Adapter extends ChatProtocolAdapter {
       let replyTo: string | undefined;
 
       if (refs.reply?.e) {
-        // Replying to another reply - show reply preview
+        // Replying to another reply
         replyTo = refs.reply.e.id;
+      } else if (refs.root?.e) {
+        // Replying directly to root
+        replyTo = refs.root.e.id;
       } else {
-        // Replying directly to root or malformed - don't show reply preview
-        // (replying to root is implied in thread chat context)
-        replyTo = undefined;
+        // Malformed or legacy reply - assume replying to root
+        replyTo = rootEventId;
       }
 
       return {