feat: 新增配送合同附件安全上传功能

- 增加合同专用 PDF 上传、鉴权预览和失败清理接口
- 支持草稿附件替换移除、并发保护和启用完整性校验
- 修复循环模板引用导致文件选择器无法打开的问题
- 补充专项测试、中文项目文档和操作日志

frontend/platform_admin/src/views/resource/ContractAttachmentField.vue

@@ -0,0 +1,169 @@
+<!--
+  功能：提供单个配送合同 PDF 附件的选择、拖拽、预览和移除控件。
+  版本：v1.0.0
+-->
+<template>
+  <div
+    class="contract-file-control"
+    :class="{ 'contract-file-disabled': disabled }"
+    :tabindex="disabled ? -1 : 0"
+    role="button"
+    :aria-disabled="disabled"
+    aria-label="选择合同附件 PDF"
+    @click="openPicker"
+    @keydown.enter.prevent="openPicker"
+    @keydown.space.prevent="openPicker"
+    @dragover.prevent
+    @drop.prevent="selectDroppedFile"
+  >
+    <input
+      ref="fileInput"
+      class="contract-file-input"
+      type="file"
+      accept=".pdf,application/pdf"
+      :disabled="disabled"
+      @change="selectPickedFile"
+    />
+    <div class="contract-file-main">
+      <icon-upload />
+      <div>
+        <strong>{{ title }}</strong>
+        <div class="contract-file-hint">点击选择或拖拽 PDF，最大 10 MiB</div>
+        <div v-if="attachment.requiresReupload" class="contract-file-warning">
+          旧附件地址不可用，请重新上传
+        </div>
+      </div>
+    </div>
+    <a-space @click.stop @keydown.stop>
+      <a-button
+        v-if="attachment.available && !attachment.selectedFile && !attachment.removed"
+        size="small"
+        @click="emit('preview')"
+      >
+        <template #icon><icon-eye /></template>预览
+      </a-button>
+      <a-button
+        v-if="attachment.selectedFile"
+        size="small"
+        @click="emit('clear-selection')"
+      >
+        取消选择
+      </a-button>
+      <a-button
+        v-else-if="attachment.hasExisting && !attachment.removed"
+        size="small"
+        status="danger"
+        @click="emit('remove')"
+      >
+        <template #icon><icon-delete /></template>移除
+      </a-button>
+    </a-space>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { IconDelete, IconEye, IconUpload } from '@arco-design/web-vue/es/icon';
+import { computed, ref } from 'vue';
+
+export type ContractAttachmentFieldState = {
+  selectedFile?: File;
+  hasExisting: boolean;
+  available: boolean;
+  requiresReupload: boolean;
+  removed: boolean;
+};
+
+const props = defineProps<{
+  attachment: ContractAttachmentFieldState;
+  disabled?: boolean;
+}>();
+
+const emit = defineEmits<{
+  select: [file: File];
+  remove: [];
+  'clear-selection': [];
+  preview: [];
+}>();
+
+const fileInput = ref<HTMLInputElement>();
+const title = computed(() => {
+  if (props.attachment.selectedFile) return props.attachment.selectedFile.name;
+  if (props.attachment.removed) return '未选择合同附件';
+  if (props.attachment.hasExisting) return '合同附件.pdf';
+  return '选择合同附件';
+});
+
+/** 打开组件内唯一的原生文件选择器。 */
+function openPicker() {
+  if (!props.disabled) fileInput.value?.click();
+}
+
+/** 读取点击选择的单个文件，并允许再次选择同名文件。 */
+function selectPickedFile(event: Event) {
+  const input = event.target as HTMLInputElement;
+  const file = input.files?.[0];
+  if (file) emit('select', file);
+  input.value = '';
+}
+
+/** 接收拖拽到控件上的第一个文件。 */
+function selectDroppedFile(event: DragEvent) {
+  if (props.disabled) return;
+  const file = event.dataTransfer?.files?.[0];
+  if (file) emit('select', file);
+}
+</script>
+
+<style scoped lang="less">
+.contract-file-control {
+  display: flex;
+  gap: 16px;
+  align-items: center;
+  justify-content: space-between;
+  min-height: 88px;
+  padding: 16px;
+  cursor: pointer;
+  border: 1px dashed var(--color-border-3);
+  border-radius: 6px;
+  outline: none;
+  transition: border-color 0.2s, background 0.2s, box-shadow 0.2s;
+}
+.contract-file-control:hover,
+.contract-file-control:focus-visible {
+  background: var(--color-fill-1);
+  border-color: rgb(var(--primary-6));
+}
+.contract-file-control:focus-visible {
+  box-shadow: 0 0 0 2px rgba(var(--primary-6), 0.2);
+}
+.contract-file-disabled {
+  cursor: not-allowed;
+  opacity: 0.65;
+}
+.contract-file-input {
+  display: none;
+}
+.contract-file-main {
+  display: flex;
+  gap: 12px;
+  align-items: center;
+  min-width: 0;
+}
+.contract-file-main strong {
+  display: block;
+  overflow: hidden;
+  color: var(--color-text-1);
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.contract-file-hint {
+  margin-top: 4px;
+  color: var(--color-text-3);
+  font-size: 12px;
+}
+.contract-file-warning {
+  margin-top: 4px;
+  color: rgb(var(--warning-6));
+  font-size: 12px;
+}
+</style>