feat 搭建架构骨架

src/composables/useIntersection.ts

@@ -0,0 +1,29 @@
+import { onMounted, onUnmounted, ref, type Ref } from 'vue'
+
+/** 元素可见性（配合图片懒加载/曝光统计） */
+export function useIntersection(
+  target: Ref<Element | null | undefined>,
+  options?: IntersectionObserverInit,
+): {
+  isVisible: Ref<boolean>
+} {
+  const isVisible = ref(false)
+  let observer: IntersectionObserver | null = null
+
+  onMounted(() => {
+    const el = target.value
+    if (!el) return
+    observer = new IntersectionObserver((entries) => {
+      const entry = entries[0]
+      if (entry) isVisible.value = entry.isIntersecting
+    }, options)
+    observer.observe(el)
+  })
+
+  onUnmounted(() => {
+    observer?.disconnect()
+    observer = null
+  })
+
+  return { isVisible }
+}