优化Pexels图片加载逻辑，当切换到背景图片标签页时才调用api获取图片

src/views/tools/add_background/add_background.vue

@@ -1209,6 +1209,7 @@ const pexelsDisplayCount = ref(12)
 const PEXELS_PER_PAGE = 80 // Fetch 80 images per API call
 const PEXELS_DISPLAY_INCREMENT = 12 // Display 12 more images each time
 const pexelsHasMore = ref(true) // Track if there are more images to fetch
+const pexelsImagesLoaded = ref(false) // Track if Pexels images have been loaded
 
 // Custom background images
 const customBackgrounds = ref<string[]>([])
@@ -1500,12 +1501,20 @@ const handleUrlSubmit = async () => {
   }
 }
 
+// Watch for tab changes to lazy load Pexels images
+watch(activeTab, (newTab) => {
+  // Lazy load Pexels images only when user switches to 'image' tab for the first time
+  if (newTab === 'image' && !pexelsImagesLoaded.value) {
+    pexelsImagesLoaded.value = true
+    fetchPexelsImages()
+  }
+})
+
 onMounted(() => {
   window.addEventListener('resize', handleResize)
   window.addEventListener('paste', handlePaste)
   loadFavoriteColors()
   loadCustomBackgrounds()
-  fetchPexelsImages()
 })
 
 onUnmounted(() => {