polish(admin): 抽出后台控件包并统一各页布局与交互

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

frontend/components/admin/AdminSettingRow.tsx

@@ -0,0 +1,36 @@
+import type { ReactNode } from "react";
+
+/** 「标题 + 说明 | 控件」一行，设置页与内容策略共用 */
+export default function AdminSettingRow({
+  title,
+  description,
+  control,
+  children,
+}: {
+  title: ReactNode;
+  description?: ReactNode;
+  control?: ReactNode;
+  /** 展开区（如阈值输入），画在分隔线下方 */
+  children?: ReactNode;
+}) {
+  return (
+    <div className="panel p-4 sm:p-5">
+      <div className="flex items-start justify-between gap-4 flex-wrap">
+        <div className="min-w-0 flex-1">
+          <h2 className="text-[15px] font-semibold flex items-center gap-1.5" style={{ color: "var(--ink)" }}>
+            {title}
+          </h2>
+          {description != null && description !== "" && (
+            <p className="meta text-[12.5px] mt-1 leading-relaxed">{description}</p>
+          )}
+        </div>
+        {control != null && <div className="shrink-0">{control}</div>}
+      </div>
+      {children != null && (
+        <div className="mt-4 pt-4" style={{ borderTop: "1px solid var(--line)" }}>
+          {children}
+        </div>
+      )}
+    </div>
+  );
+}