feat(文件预览): 添加对PDF、Word和Excel文件的预览支持

添加新的文件预览组件，支持PDF、Word(docx)、Excel(xlsx/xls)文件类型预览
重构图片预览为独立组件，并添加相关依赖包

klp-ui/src/components/FilePreview/preview/xlsx/index.vue

@@ -0,0 +1,38 @@
+<template>
+  <div class="xlsx-preview">
+    <vue-office-excel :src="src" @render-error="handleExcelError" />
+  </div>
+</template>
+
+<script>
+import VueOfficeExcel from '@vue-office/excel';
+import '@vue-office/excel/lib/index.css';
+
+export default {
+  name: "XlsxPreview",
+  components: {
+    VueOfficeExcel
+  },
+  props: {
+    src: {
+      type: String,
+      required: true,
+      description: "Excel文件的URL或路径"
+    }
+  },
+  methods: {
+    handleExcelError(err) {
+      console.error('excel预览失败:', err);
+      this.$message.error('Excel预览失败，请下载查看');
+    }
+  }
+};
+</script>
+
+<style scoped>
+.xlsx-preview {
+  width: 100%;
+  height: 70vh;
+  overflow-y: auto;
+}
+</style>