feat: 结果页添加帧预览、GIF动画和导出选项

- 后端: GetAssets 返回素材级别 metadata，区分 frame/preview/spritesheet 类型
- 后端: 上传时区分素材类型标签，GIF URL 独立追踪
- 前端: 结果详情页默认展示拆分后的单帧网格
- 前端: 添加动作帧 GIF 预览弹窗
- 前端: 添加导出下拉菜单（整张精灵表/自动切分帧）
- 前端: 失败任务展示错误信息和重试次数

frontend/src/api/generate.ts

@@ -19,18 +19,31 @@ export async function getTask(taskId: string): Promise<Task> {
 
 export async function getAssets(taskId: string): Promise<Asset[]> {
   const resp = await get<AssetsResponse>(`/api/v1/tasks/${taskId}/assets`)
-  return resp.assets.map((a, i) => ({
-    id: `asset-${i}`,
-    key: a.key,
-    url: `/api/v1/assets/download?key=${encodeURIComponent(a.key)}`,
-    format: a.format,
-    width: resp.metadata.frameWidth,
-    height: resp.metadata.frameHeight,
-    metadata: {
-      frameWidth: resp.metadata.frameWidth,
-      frameHeight: resp.metadata.frameHeight,
-      frameCount: resp.metadata.frameCount,
-      directions: resp.metadata.directions,
-    },
-  }))
+  return resp.assets.map((a, i) => {
+    let assetType: Asset['assetType'] = 'frame'
+    let index = i
+    try {
+      const meta = JSON.parse(a.metadata)
+      if (meta.type) assetType = meta.type
+      if (typeof meta.index === 'number') index = meta.index
+    } catch { /* use defaults */ }
+
+    return {
+      id: `asset-${i}`,
+      key: a.key,
+      url: `/api/v1/assets/download?key=${encodeURIComponent(a.key)}`,
+      format: a.format,
+      width: resp.metadata.frameWidth,
+      height: resp.metadata.frameHeight,
+      assetType,
+      index,
+      metadata: {
+        frameWidth: resp.metadata.frameWidth,
+        frameHeight: resp.metadata.frameHeight,
+        frameCount: resp.metadata.frameCount,
+        directions: resp.metadata.directions,
+        gifUrl: resp.metadata.gifUrl,
+      },
+    }
+  })
 }

frontend/src/api/mock.ts

@@ -115,6 +115,8 @@ const MOCK_ASSETS: Asset[] = [
     format: 'png',
     width: 256,
     height: 256,
+    assetType: 'frame',
+    index: 0,
     metadata: {
       frameWidth: 64,
       frameHeight: 64,

frontend/src/api/types.ts

@@ -87,12 +87,15 @@ export interface Asset {
   format: string
   width: number
   height: number
+  assetType: 'frame' | 'preview' | 'spritesheet'
   metadata: {
     frameWidth?: number
     frameHeight?: number
     frameCount?: number
     directions?: number
+    gifUrl?: string
   }
+  index: number
 }
 
 // 生成请求 — 对应 POST /api/v1/generate
@@ -121,6 +124,7 @@ export interface AssetsResponse {
     key: string
     url: string
     format: string
+    metadata: string // JSON: {"index":0,"type":"frame"|"preview"|"spritesheet"}
   }[]
   metadata: {
     frameWidth: number