fix(web): currentPersona 稳定加载——不再因 mount 时无 token/一次失败就退回默认头像

- useAppStore.partialize 持久化 currentPersona：刷新后保持本角色头像/背景
- App.tsx：token 出现即重拉 + 失败 3s 重试，替代一次性 mount 拉取
- 红线：仍只显示当前角色自己的头像/背景，绝不 fallback 其它角色

frontend/web/src/store/useAppStore.ts

@@ -256,6 +256,10 @@ export const useAppStore = create<AppStore>()(
         mood: s.mood,
         context: s.context,
         backthink: s.backthink,
+        // Persist the resolved persona so a refresh keeps showing THIS persona's
+        // own avatar/background — never falling back to a neutral placeholder or
+        // (worse) another role's image because the mount-time fetch missed.
+        currentPersona: s.currentPersona,
       }),
     }
   )