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/hooks.ts

@@ -8,21 +8,25 @@ import {
   loadLeaderboardSettings,
   loadPrivateSquareStatus,
   loadPromptPrefixSettings,
+  loadPublishSquares,
   updateAppearanceSettings,
   updateCitationDisplaySettings,
   updateLeaderboardSettings,
   updatePrivateSquareSettings,
   updatePromptPrefixSettings,
+  updatePublishSquares,
   type AppearanceUpdate,
   type CitationDisplayUpdate,
   type LeaderboardSettingsUpdate,
   type PrivateSquareUpdate,
   type PromptPrefixUpdate,
+  type PublishSquaresUpdate,
   type ViewMode,
 } from "./api";
 
 const PROMPT_PREFIX_KEY = ["systemSettings", "promptPrefix"] as const;
 const PRIVATE_SQUARE_KEY = ["systemSettings", "privateSquare"] as const;
+const PUBLISH_SQUARES_KEY = ["systemSettings", "publishSquares"] as const;
 const APPEARANCE_KEY = ["systemSettings", "appearance"] as const;
 const CITATION_DISPLAY_KEY = ["systemSettings", "citationDisplay"] as const;
 const LEADERBOARD_KEY = ["systemSettings", "leaderboard"] as const;
@@ -67,6 +71,31 @@ export function useUpdatePrivateSquareSettings() {
   });
 }
 
+/** The configured publish squares (发布广场). Readable by any logged-in user —
+ * the gallery sub-tabs and the publish-flow square picker both need it. */
+export function usePublishSquares() {
+  return useQuery({
+    queryKey: PUBLISH_SQUARES_KEY,
+    queryFn: () => loadPublishSquares(),
+    staleTime: 60_000,
+    refetchOnWindowFocus: false,
+    retry: false,
+  });
+}
+
+export function useUpdatePublishSquares() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: (body: PublishSquaresUpdate) => updatePublishSquares(body),
+    onSuccess: (data) => {
+      queryClient.setQueryData(PUBLISH_SQUARES_KEY, data);
+      // Squares changing can re-bucket gallery tabs; refresh agent/skill lists.
+      queryClient.invalidateQueries({ queryKey: ["agents"] });
+      queryClient.invalidateQueries({ queryKey: ["skills"] });
+    },
+  });
+}
+
 export function useAppearanceSettings() {
   return useQuery({
     queryKey: APPEARANCE_KEY,