feat(folders): 完善公开文件夹功能 - 添加 /explore 和 /favorites 页面

- 新增 /explore 页面：浏览和搜索公开文件夹
- 新增 /explore/[id] 页面：以只读模式查看公开文件夹
- 新增 /favorites 页面：管理收藏的文件夹
- 重构 /folders 页面：仅显示当前用户的文件夹
- 更新导航栏：添加 Explore 和 Favorites 链接
- 添加 i18n 翻译：explore 和 favorites 相关文本
- 更新 AGENTS.md：添加数据库迁移规范（必须使用 migrate dev）

src/app/(features)/favorites/FavoritesClient.tsx

@@ -0,0 +1,116 @@
+"use client";
+
+import {
+  ChevronRight,
+  Folder as Fd,
+  Heart,
+} from "lucide-react";
+import { useEffect, useState } from "react";
+import { useRouter } from "next/navigation";
+import { useTranslations } from "next-intl";
+import { PageLayout } from "@/components/ui/PageLayout";
+import { PageHeader } from "@/components/ui/PageHeader";
+import { CardList } from "@/components/ui/CardList";
+import { actionGetUserFavorites } from "@/modules/folder/folder-aciton";
+
+type UserFavorite = {
+  id: number;
+  folderId: number;
+  folderName: string;
+  folderCreatedAt: Date;
+  folderTotalPairs: number;
+  folderOwnerId: string;
+  folderOwnerName: string | null;
+  folderOwnerUsername: string | null;
+  favoritedAt: Date;
+};
+
+interface FavoriteCardProps {
+  favorite: UserFavorite;
+}
+
+const FavoriteCard = ({ favorite }: FavoriteCardProps) => {
+  const router = useRouter();
+  const t = useTranslations("favorites");
+
+  return (
+    <div
+      className="flex justify-between items-center group py-4 px-5 border-b border-gray-200 last:border-b-0 hover:bg-gray-50 cursor-pointer transition-colors"
+      onClick={() => {
+        router.push(`/explore/${favorite.folderId}`);
+      }}
+    >
+      <div className="flex items-center gap-4 flex-1">
+        <div className="shrink-0 text-primary-500">
+          <Fd size={24} />
+        </div>
+
+        <div className="flex-1 min-w-0">
+          <h3 className="font-semibold text-gray-900 truncate">{favorite.folderName}</h3>
+          <p className="text-sm text-gray-500 mt-0.5">
+            {t("folderInfo", {
+              userName: favorite.folderOwnerName ?? favorite.folderOwnerUsername ?? t("unknownUser"),
+              totalPairs: favorite.folderTotalPairs,
+            })}
+          </p>
+        </div>
+      </div>
+
+      <div className="flex items-center gap-2">
+        <Heart size={18} className="fill-red-500 text-red-500" />
+        <ChevronRight size={20} className="text-gray-400" />
+      </div>
+    </div>
+  );
+};
+
+interface FavoritesClientProps {
+  userId: string;
+}
+
+export function FavoritesClient({ userId }: FavoritesClientProps) {
+  const t = useTranslations("favorites");
+  const [favorites, setFavorites] = useState<UserFavorite[]>([]);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    loadFavorites();
+  }, [userId]);
+
+  const loadFavorites = async () => {
+    setLoading(true);
+    const result = await actionGetUserFavorites();
+    if (result.success && result.data) {
+      setFavorites(result.data);
+    }
+    setLoading(false);
+  };
+
+  return (
+    <PageLayout>
+      <PageHeader title={t("title")} subtitle={t("subtitle")} />
+
+      <div className="mt-4">
+        <CardList>
+          {loading ? (
+            <div className="p-8 text-center">
+              <div className="w-8 h-8 border-2 border-gray-200 border-t-gray-400 rounded-full animate-spin mx-auto mb-3"></div>
+              <p className="text-sm text-gray-500">{t("loading")}</p>
+            </div>
+          ) : favorites.length === 0 ? (
+            <div className="text-center py-12 text-gray-400">
+              <div className="w-16 h-16 mx-auto mb-3 rounded-full bg-gray-100 flex items-center justify-center">
+                <Heart size={24} className="text-gray-400" />
+              </div>
+              <p className="text-sm">{t("noFavorites")}</p>
+            </div>
+          ) : (
+            favorites.map((favorite) => (
+              <FavoriteCard key={favorite.id} favorite={favorite} />
+            ))
+          )}
+        </CardList>
+      </div>
+    </PageLayout>
+  );
+}