feat(web): tree batch auto-expand with depth limit and view icons

勾选文件树文件夹时自动展开并懒加载子节点，按最大深度（默认 4，勾选文件夹为第 0 层）递归收集可下载文件；触及上限时中文提示部分文件已跳过。树侧栏顶部增加显眼的批量下载入口。Home/ShowList 窗格与文件树切换增加 Font Awesome 图标。

Co-authored-by: qaiu <[email protected]>

web-front/src/components/ViewModeSwitch.vue

@@ -0,0 +1,65 @@
+<template>
+  <el-radio-group
+    :model-value="modelValue"
+    size="small"
+    class="view-mode-switch"
+    @update:model-value="$emit('update:modelValue', $event)"
+  >
+    <el-radio-button label="pane" title="窗格视图">
+      <i class="fas fa-th" aria-hidden="true"></i>
+      <span class="view-mode-text">{{ paneLabel }}</span>
+    </el-radio-button>
+    <el-radio-button label="tree" title="文件树视图">
+      <i class="fas fa-sitemap" aria-hidden="true"></i>
+      <span class="view-mode-text">{{ treeLabel }}</span>
+    </el-radio-button>
+  </el-radio-group>
+</template>
+
+<script>
+export default {
+  name: 'ViewModeSwitch',
+  props: {
+    modelValue: {
+      type: String,
+      default: 'pane'
+    },
+    paneLabel: {
+      type: String,
+      default: '窗格'
+    },
+    treeLabel: {
+      type: String,
+      default: '文件树'
+    }
+  },
+  emits: ['update:modelValue']
+}
+</script>
+
+<style scoped>
+.view-mode-switch :deep(.el-radio-button__inner) {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  gap: 6px;
+  min-height: 36px;
+  min-width: 76px;
+  padding: 8px 12px;
+}
+.view-mode-switch i {
+  font-size: 14px;
+  line-height: 1;
+}
+.view-mode-text {
+  line-height: 1;
+}
+
+@media (max-width: 480px) {
+  .view-mode-switch :deep(.el-radio-button__inner) {
+    min-width: 68px;
+    min-height: 40px;
+    padding: 10px 12px;
+  }
+}
+</style>