feat(auth): 为未登录用户添加登录引导界面

为目标页面、营养记录、食物添加等功能添加登录状态检查和引导界面，确保用户在未登录状态下能够获得清晰的登录提示和指引。

- 在目标页面添加精美的未登录引导界面，包含渐变背景和登录按钮
- 为食物记录相关组件添加登录状态检查，未登录时自动跳转登录页面
- 重构血氧饱和度卡片为独立数据获取，移除对外部数据依赖
- 移除个人页面的实验性SwiftUI组件，统一使用原生TouchableOpacity
- 清理统计页面和营养记录页面的冗余代码和未使用变量

components/FloatingFoodOverlay.tsx

@@ -1,4 +1,5 @@
 import { ROUTES } from '@/constants/Routes';
+import { useAuthGuard } from '@/hooks/useAuthGuard';
 import { Ionicons } from '@expo/vector-icons';
 import { BlurView } from 'expo-blur';
 import { useRouter } from 'expo-router';
@@ -20,19 +21,21 @@ interface FloatingFoodOverlayProps {
 export function FloatingFoodOverlay({ visible, onClose, mealType = 'dinner' }: FloatingFoodOverlayProps) {
   const router = useRouter();
 
+  const { pushIfAuthedElseLogin } = useAuthGuard()
+
   const handleFoodLibrary = () => {
     onClose();
-    router.push(`${ROUTES.FOOD_LIBRARY}?mealType=${mealType}`);
+    pushIfAuthedElseLogin(`${ROUTES.FOOD_LIBRARY}?mealType=${mealType}`);
   };
 
   const handlePhotoRecognition = () => {
     onClose();
-    router.push(`/food/camera?mealType=${mealType}`);
+    pushIfAuthedElseLogin(`/food/camera?mealType=${mealType}`);
   };
 
   const handleVoiceRecord = () => {
     onClose();
-    router.push(`${ROUTES.VOICE_RECORD}?mealType=${mealType}`);
+    pushIfAuthedElseLogin(`${ROUTES.VOICE_RECORD}?mealType=${mealType}`);
   };
 
   const menuItems = [