feat(food): 添加拍摄指引弹窗与相册选择功能

- 在相机界面新增“拍摄示例”弹窗，展示正确/错误拍摄对比图
- 底部控制栏增加相册选择按钮与帮助按钮
- 优化控制栏布局为左右分布，提升操作便捷性
- 移除 food-recognition 中冗余的 isUploading 状态，简化上传流程

app/food/food-recognition.tsx

@@ -29,8 +29,7 @@ export default function FoodRecognitionScreen() {
   }>();
 
   const { imageUri, mealType } = params;
-  const { upload, uploading } = useCosUpload();
-  const [isUploading, setIsUploading] = useState(false);
+  const { upload } = useCosUpload();
   const [showRecognitionProcess, setShowRecognitionProcess] = useState(false);
   const [recognitionLogs, setRecognitionLogs] = useState<string[]>([]);
   const [currentStep, setCurrentStep] = useState<'idle' | 'uploading' | 'recognizing' | 'completed' | 'failed'>('idle');
@@ -128,7 +127,6 @@ export default function FoodRecognitionScreen() {
       setShowRecognitionProcess(true);
       setRecognitionLogs([]);
       setCurrentStep('uploading');
-      setIsUploading(true);
       dispatch(setLoading(true));
 
       addLog('📤 正在上传图片到云端...');
@@ -167,7 +165,7 @@ export default function FoodRecognitionScreen() {
       const recognitionId = `recognition_${Date.now()}_${Math.random().toString(36).slice(2, 8)}`;
 
       // 保存识别结果到 Redux
-      await dispatch(saveRecognitionResult({
+      dispatch(saveRecognitionResult({
         id: recognitionId,
         result: recognitionResult
       }));
@@ -184,7 +182,6 @@ export default function FoodRecognitionScreen() {
       setCurrentStep('failed');
       dispatch(setError('食物识别失败，请重试'));
     } finally {
-      setIsUploading(false);
       dispatch(setLoading(false));
     }
   };