fix: include event pointer when zapping chat messages

Pass the message event as eventPointer when opening ZapWindow from
chat context menu. This enables:
- Event preview in the zap window
- Proper window title showing "Zap [username]"

src/components/chat/ChatMessageContextMenu.tsx

@@ -155,6 +155,8 @@ export function ChatMessageContextMenu({
       recipientPubkey: zapConfig.recipientPubkey,
       customTags: zapConfig.customTags,
       relays: zapConfig.relays,
+      // Include the message event as context for zap preview
+      eventPointer: { id: event.id, author: event.pubkey },
     });
   };