feat: user personalization with Honcho-backed preferences

- WelcomeScreen: first-time name entry with cute onboarding
- identify WS message: sets user_id, loads saved prefs from Honcho
- set_preference WS message: saves scene/outfit/accessory to Honcho metadata
- Preferences auto-load on return visits via localStorage + Honcho peer meta
- Kira uses the user's name in greeting and prompts
- Backend: get/set preference methods in KiraMemory service
- Frontend: optimistic preference updates, synced to backend on change

frontend/src/components/ChatBubble.tsx

@@ -4,11 +4,13 @@ interface Message {
   id: string;
   role: 'user' | 'kira';
   text: string;
+  timestamp: number;
 }
 
 interface Props {
   messages: Message[];
   isKiraSpeaking: boolean;
+  userName?: string;
 }
 
 export default function ChatBubble({ messages, isKiraSpeaking }: Props) {