feat: 重构应用加载流程和动画管理

- 新增 AppLoader 组件作为全局加载器
- 引入 Pinia 状态管理应用加载状态
- 创建 usePageScrollLock 组合式函数管理滚动锁定
- 重构首页动画流程，使用 Promise 链式调用
- 移除旧的 HomeLoader 组件
- 优化头部导航栏的入场动画触发逻辑

app/composables/usePageScrollLock.ts

@@ -0,0 +1,50 @@
+import { onMounted, onBeforeUnmount, watch, type Ref } from 'vue'
+import { useNuxtApp } from '#app'
+import type Lenis from 'lenis'
+import { useAppStore } from '~/stores/app'
+
+export const usePageScrollLock = (isLocked: Ref<boolean> | boolean) => {
+  const { $lenis } = useNuxtApp() as ReturnType<typeof useNuxtApp> & { $lenis?: Lenis }
+  
+  const lockScroll = () => {
+    if (import.meta.client) {
+      document.documentElement.classList.add('is-home-intro-active')
+      $lenis?.scrollTo(0, { immediate: true })
+      $lenis?.stop()
+    }
+  }
+
+  const unlockScroll = () => {
+    if (import.meta.client) {
+      document.documentElement.classList.remove('is-home-intro-active')
+      $lenis?.start()
+    }
+  }
+
+  // If passed a boolean, lock immediately and unlock on unmount
+  if (typeof isLocked === 'boolean') {
+    if (isLocked) {
+      onMounted(() => {
+        lockScroll()
+      })
+      onBeforeUnmount(() => {
+        unlockScroll()
+      })
+    }
+  } else {
+    // If passed a ref, watch its value
+    watch(isLocked, (locked) => {
+      if (locked) {
+        lockScroll()
+      } else {
+        unlockScroll()
+      }
+    }, { immediate: true })
+    
+    onBeforeUnmount(() => {
+      unlockScroll()
+    })
+  }
+
+  return { lockScroll, unlockScroll }
+}