feat(assets): 分页查询 + voice 默认素材库自动初始化

- GET /assets 增加 skip/limit 分页参数，响应包含 total/skip/limit
- GET /asset-libraries 增加 kind 过滤参数
- 新增 POST /asset-libraries/ensure-default 自动创建默认素材库
- 前端上传配音音频走通用上传链路（无缺口）

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/web/src/api/assets.ts

@@ -129,6 +129,35 @@ export const getAssets = async (libraryId: string): Promise<AssetItem[]> => {
   return response.data.items || [];
 };
 
+/** 按类型获取素材（如 voice/video/image） */
+export const getAssetsByKind = async (kind: string): Promise<AssetItem[]> => {
+  const response = await apiClient.get("/assets", {
+    params: { kind },
+  });
+  return response.data.items || [];
+};
+
+/** 创建素材（上传文件后调用，附带 metadata） */
+export const createAsset = async (data: {
+  library_id: string;
+  name: string;
+  storage_key: string;
+  mime_type: string;
+  metadata?: Record<string, unknown>;
+}): Promise<AssetItem> => {
+  const response = await apiClient.post("/assets", data);
+  return response.data;
+};
+
+/** 更新素材（名称、metadata 等） */
+export const updateAsset = async (
+  assetId: string,
+  data: { name?: string; metadata?: Record<string, unknown> },
+): Promise<AssetItem> => {
+  const response = await apiClient.put(`/assets/${assetId}`, data);
+  return response.data;
+};
+
 /** 更新素材审核状态 */
 export const updateAssetReviewStatus = async (
   assetId: string,