refactor(ui): 优化药品添加页面的图片选择和显示效果

app/medications/add-medication.tsx

@@ -432,8 +432,7 @@ export default function AddMedicationScreen() {
               }
 
               const result = await ImagePicker.launchImageLibraryAsync({
-                allowsEditing: true,
-                mediaTypes: ImagePicker.MediaTypeOptions.Images,
+                mediaTypes: ['images'],
                 quality: 0.9,
               });
 
@@ -651,7 +650,7 @@ export default function AddMedicationScreen() {
             >
               {photoPreview ? (
                 <>
-                  <Image source={{ uri: photoPreview }} style={styles.photoPreview} contentFit="cover" />
+                  <Image source={{ uri: photoPreview }} style={styles.photoPreview} contentFit="contain" />
                   <View style={styles.photoOverlay}>
                     <Ionicons name="camera" size={18} color="#fff" />
                     <ThemedText style={styles.photoOverlayText}>
@@ -1370,7 +1369,7 @@ const styles = StyleSheet.create({
   photoCard: {
     borderWidth: 1,
     borderRadius: 20,
-    height: 180,
+    height: 240,
     overflow: 'hidden',
     justifyContent: 'center',
   },