perf(core): 项目列表改轻量序列化 + 计数走真实 count,根治刷新 2-3s

/api/projects/ 列表此前与详情共用重序列化器(嵌套 阶段/片段/故事板/时间线 + 每资产算 url),
20 个项目把全套关联拉出 → 实测 ~2-3s,正是每次刷新慢的主因。

- 新增 ProjectListSerializer(轻:名/状态/阶段/product/封面/脚本数/镜数);
  ProjectViewSet.get_serializer_class 列表用轻的、详情用全量;
  get_queryset 列表走轻查询(select_related product + annotate 计数,不做那串 12 个重 prefetch)。
  实测 /api/projects/ 2-3s → 0.48s。
- 新增 /api/projects/summary/(total + by_status,只跑 COUNT,不拉项目对象)。
- 计数显示(侧栏徽标 / 仪表盘 总项目·SKU·N 个)改用分页响应的真实 count(productTotal/projectTotal),
  不再用「已加载 20 条」的长度;projects 列表页脚本状态/镜数改读 *_count 字段。

闸:9 页全绿、无瀑布、API 全过;projects 端点提速 ~5x。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

core/frontend/src/routes/projects.tsx

@@ -528,7 +528,7 @@ export function ProjectsPage({ products, projects, navigate, openPipeline, onDel
     if (!`${project.name} ${productTitle(project.product)}`.toLowerCase().includes(query.toLowerCase())) return false;
     if (catFilter && productCat(project.product) !== catFilter) return false;
     if (sourceFilter !== "all") {
-      const hasScript = (project.script_versions?.length || 0) > 0;
+      const hasScript = (project.script_version_count ?? project.script_versions?.length ?? 0) > 0;
       if (sourceFilter === "has" && !hasScript) return false;
       if (sourceFilter === "none" && hasScript) return false;
     }
@@ -663,7 +663,7 @@ export function ProjectsPage({ products, projects, navigate, openPipeline, onDel
             <tbody id="list-tbody">
               {pageItems.map((project) => {
                 const no = projStageNo(project);
-                const shots = project.video_segments.length || 4;
+                const shots = project.video_segment_count ?? project.video_segments?.length ?? 4;
                 const cover = projCover(project.name);
                 return (
                   <tr key={project.id} data-status={projBucket(project)} data-name={project.name} onClick={() => openPipeline(project.id)}>
@@ -674,7 +674,7 @@ export function ProjectsPage({ products, projects, navigate, openPipeline, onDel
                       </div>
                     </td>
                     <td>{productTitle(project.product)}</td>
-                    <td><span className="muted">{(project.script_versions?.length || 0) > 0 ? "AI 已生成" : "暂无脚本"}</span></td>
+                    <td><span className="muted">{(project.script_version_count ?? project.script_versions?.length ?? 0) > 0 ? "AI 已生成" : "暂无脚本"}</span></td>
                     <td>
                       <div className="hstack">
                         <div className="prog">{[1, 2, 3, 4, 5].map((i) => <span key={i} className={i < no ? "done" : i === no ? "cur" : ""} />)}</div>