feat(square): 新增发布广场功能，智能体/技能按广场分类展示

- 后端新增 PublishSquare/PublishSquaresSettings 配置与读写接口
- agents/skills 增加 square_id 字段及对应迁移脚本
- 前端新增发布广场设置页、技能转移选择器，画廊按广场分 Tab 展示
- lead_agent prompt 及若干持久化层适配调整

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/core/system-settings/api.ts

@@ -89,6 +89,52 @@ export async function loadPrivateSquareStatus(): Promise<PrivateSquareStatus> {
   return (await response.json()) as PrivateSquareStatus;
 }
 
+export interface PublishSquare {
+  id: string;
+  name: string;
+  description: string;
+}
+
+export interface PublishSquaresSettings {
+  squares: PublishSquare[];
+  default_square_id: string;
+}
+
+export interface PublishSquaresUpdate {
+  squares?: PublishSquare[];
+  default_square_id?: string;
+}
+
+export async function loadPublishSquares(): Promise<PublishSquaresSettings> {
+  const response = await apiFetch(
+    `${getBackendBaseURL()}/api/system-settings/publish-squares`,
+  );
+  if (!response.ok) {
+    throw new Error(`Failed to load publish squares: ${response.status}`);
+  }
+  return (await response.json()) as PublishSquaresSettings;
+}
+
+export async function updatePublishSquares(
+  body: PublishSquaresUpdate,
+): Promise<PublishSquaresSettings> {
+  const response = await apiFetch(
+    `${getBackendBaseURL()}/api/system-settings/publish-squares`,
+    {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify(body),
+    },
+  );
+  if (!response.ok) {
+    const detail = await response
+      .json()
+      .catch(() => ({ detail: "Failed to update publish squares" }));
+    throw new Error(detail.detail ?? "Failed to update publish squares");
+  }
+  return (await response.json()) as PublishSquaresSettings;
+}
+
 export type ThemeMode = "light" | "dark";
 export type ViewMode = "card" | "list";