feat: add ONLYOFFICE document preview for contract attachments

DocumentPreviewController provides preview config and file streaming endpoints. ContractDetailView adds 'preview' button to attachment list and opens ONLYOFFICE iframe dialog.

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

web/delivery-platform-ui/src/views/ContractDetailView.vue

@@ -86,9 +86,18 @@
             <template #default="{ row }">{{ (row.fileSize / 1024).toFixed(1) }} KB</template>
           </el-table-column>
           <el-table-column prop="createdAt" label="上传时间" width="170" />
+          <el-table-column label="操作" width="80" fixed="right">
+            <template #default="{ row }">
+              <el-button type="primary" link @click="previewAttachment(row)">预览</el-button>
+            </template>
+          </el-table-column>
         </el-table>
       </div>
 
+    <el-dialog v-model="previewDialogVisible" :title="previewTitle" width="90%" top="5vh" destroy-on-close>
+      <iframe :src="previewUrl" style="width:100%;height:75vh;border:none;border-radius:4px" />
+    </el-dialog>
+
       <h3 class="section-title">最近审计</h3>
       <el-table v-loading="auditLoading" :data="auditRows" border stripe size="small" style="width: 100%">
         <el-table-column label="时间" width="180">
@@ -169,6 +178,15 @@ const auditRows = ref([]);
 
 const attachments = ref([]);
 const uploading = ref(false);
+const previewDialogVisible = ref(false);
+const previewUrl = ref("");
+const previewTitle = ref("");
+
+function previewAttachment(row) {
+  previewTitle.value = row.fileName || "预览";
+  previewUrl.value = `${window.location.origin}/api/v1/preview/${row.id}`;
+  previewDialogVisible.value = true;
+}
 
 const lineDialogVisible = ref(false);
 const lineEditingId = ref(null);
@@ -307,8 +325,8 @@ function formatAuditTime(row) {
 async function loadNameMaps() {
   try {
     const [cRes, pRes] = await Promise.all([
-      listCustomers({ page: 0, size: 500 }),
-      listProjects({ page: 0, size: 500 }),
+      listCustomers({ page: 0, size: 200 }),
+      listProjects({ page: 0, size: 200 }),
     ]);
     const cBody = cRes.data && typeof cRes.data === "object" ? cRes.data : {};
     const pBody = pRes.data && typeof pRes.data === "object" ? pRes.data : {};