feat: 公开嵌入页主题支持外部指定 + 排行榜入口移至左上角

- 公开页(/share、/public、/roundtable-share)新增 ?theme= 与
  deerflow:set-theme postMessage 两种外部主题指定方式,经
  usePublicEmbedTheme 接成 next-themes forcedTheme,不写 localStorage
- 排行榜入口从欢迎语旁移到 workspace-header 左上角应用名旁
- 新增 docs/embed-public-pages-theme.md 嵌入主题使用文档

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

frontend-web/src/components/workspace/welcome.tsx

@@ -1,6 +1,5 @@
 "use client";
 
-import { Trophy } from "lucide-react";
 import { useSearchParams } from "next/navigation";
 import { useEffect, useMemo } from "react";
 
@@ -8,7 +7,6 @@ import { useI18n } from "@/core/i18n/hooks";
 import { cn } from "@/lib/utils";
 
 import { AuroraText } from "../ui/aurora-text";
-import { Button } from "../ui/button";
 
 let waved = false;
 
@@ -47,20 +45,6 @@ export function Welcome({
               {isUltra ? "🚀" : "👋"}
             </div>
             <AuroraText colors={colors}>{t.welcome.greeting}</AuroraText>
-            {/* 用户排行榜入口:紧挨欢迎语的"CM助手",新标签打开免登录的公开排行榜页。 */}
-            <Button
-              type="button"
-              variant="ghost"
-              size="sm"
-              onClick={() =>
-                window.open("#/public/leaderboard", "_blank", "noopener")
-              }
-              title="打开用户排行榜公开页"
-              className="text-muted-foreground hover:text-foreground h-8 shrink-0 gap-1.5 px-2 text-xs font-medium"
-            >
-              <Trophy className="size-4" />
-              <span>排行榜</span>
-            </Button>
           </div>
         )}
       </div>

frontend-web/src/components/workspace/workspace-header.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { ChevronLeft, ChevronRight } from "lucide-react";
+import { ChevronLeft, ChevronRight, Trophy } from "lucide-react";
 import Link from "next/link";
 
 import { Button } from "@/components/ui/button";
@@ -86,6 +86,20 @@ export function WorkspaceHeader({ className }: { className?: string }) {
           ) : (
             titleBlock
           )}
+          {/* 用户排行榜入口:紧挨左上角的应用名,新标签打开免登录的公开排行榜页。 */}
+          <Button
+            type="button"
+            variant="ghost"
+            size="sm"
+            onClick={() =>
+              window.open("#/public/leaderboard", "_blank", "noopener")
+            }
+            title="打开用户排行榜公开页"
+            className="text-muted-foreground hover:text-sidebar-foreground h-8 shrink-0 gap-1 px-1.5 text-xs font-medium"
+          >
+            <Trophy className="size-4" />
+            <span>排行榜</span>
+          </Button>
           <SidebarCollapseButton />
         </div>
       )}