chore: 去掉未上线前的旧兼容垫片，板块流收口到首页

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Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/home/WorkspaceNav.tsx

@@ -2,7 +2,7 @@
 
 import Link from "next/link";
 import { useSearchParams } from "next/navigation";
-import { PenSquare, Home, ChevronRight } from "lucide-react";
+import { PenSquare, Home } from "lucide-react";
 import type { BoardWithCount, User } from "@/lib/api";
 
 // 首页壳内板块切换：仅替换中栏帖子流，不离开工作台
@@ -34,26 +34,14 @@ export function WorkspaceNav({ boards }: { boards: BoardWithCount[]; user?: User
           </Link>
         </div>
 
-        {/* 板块目录：标题可点击进入板块汇总列表页（/boards）；
-            下方板块卡片点击不离开工作台，仅在中栏筛选该板块帖子流 */}
+        {/* 板块目录：纯分区标题；下方卡片仅在中栏筛选该板帖子流 */}
         <div>
-          <Link
-            href="/boards"
-            className="group px-1 mb-2 flex items-center justify-between text-[11.5px] font-medium tracking-[0.08em] uppercase text-[var(--ink-3)] hover:text-[var(--accent)] transition-colors"
-            aria-label="进入板块目录列表页"
-          >
-            <span className="flex items-center">
-              <span>板块目录</span>
-              <ChevronRight
-                size={12}
-                className="ml-0.5 opacity-0 -translate-x-0.5 group-hover:opacity-100 group-hover:translate-x-0 transition-all"
-                aria-hidden="true"
-              />
-            </span>
+          <div className="px-1 mb-2 flex items-center justify-between text-[11.5px] font-medium tracking-[0.08em] uppercase text-[var(--ink-3)]">
+            <span>板块目录</span>
             {boards.length > 0 && (
               <span className="tracking-normal tabular-nums">{boards.length} 个</span>
             )}
-          </Link>
+          </div>
           <div className="space-y-2">
             {boards.map((b, i) => (
               <Link