refactor: 完全重构为 Anki 兼容数据结构

- 用 Deck 替换 Folder
- 用 Note + Card 替换 Pair (双向复习)
- 添加 NoteType (卡片模板)
- 添加 Revlog (复习历史)
- 实现 SM-2 间隔重复算法
- 更新所有前端页面
- 添加数据库迁移

src/app/(features)/memorize/DeckSelector.tsx

@@ -0,0 +1,114 @@
+"use client";
+
+import { useRouter } from "next/navigation";
+import { useTranslations } from "next-intl";
+import Link from "next/link";
+import { Layers } from "lucide-react";
+import type { ActionOutputDeck } from "@/modules/deck/deck-action-dto";
+import type { ActionOutputCardStats } from "@/modules/card/card-action-dto";
+import { PageLayout } from "@/components/ui/PageLayout";
+import { PrimaryButton } from "@/design-system/base/button";
+
+interface DeckWithStats extends ActionOutputDeck {
+  stats?: ActionOutputCardStats;
+}
+
+interface DeckSelectorProps {
+  decks: ActionOutputDeck[];
+  deckStats: Map<number, ActionOutputCardStats | undefined>;
+}
+
+const DeckSelector: React.FC<DeckSelectorProps> = ({ decks, deckStats }) => {
+  const t = useTranslations("memorize.deck_selector");
+  const router = useRouter();
+
+  const formatCardStats = (stats: ActionOutputCardStats | undefined): string => {
+    if (!stats) return t("noCards");
+    const parts: string[] = [];
+    if (stats.new > 0) parts.push(`${t("new")}: ${stats.new}`);
+    if (stats.learning > 0) parts.push(`${t("learning")}: ${stats.learning}`);
+    if (stats.review > 0) parts.push(`${t("review")}: ${stats.review}`);
+    if (stats.due > 0) parts.push(`${t("due")}: ${stats.due}`);
+    return parts.length > 0 ? parts.join(" • ") : t("noCards");
+  };
+
+  const getDueCount = (deckId: number): number => {
+    const stats = deckStats.get(deckId);
+    return stats?.due ?? 0;
+  };
+
+  return (
+    <PageLayout>
+      {decks.length === 0 ? (
+        <div className="text-center">
+          <h1 className="text-2xl md:text-3xl font-bold text-gray-800 mb-4">
+            {t("noDecks")}
+          </h1>
+          <Link href="/decks">
+            <PrimaryButton className="px-6 py-2">
+              {t("goToDecks")}
+            </PrimaryButton>
+          </Link>
+        </div>
+      ) : (
+        <>
+          <h1 className="text-2xl md:text-3xl font-bold text-gray-800 mb-6">
+            {t("selectDeck")}
+          </h1>
+          <div className="border border-gray-200 rounded-lg max-h-96 overflow-y-auto">
+            {decks
+              .toSorted((a, b) => a.id - b.id)
+              .map((deck) => {
+                const stats = deckStats.get(deck.id);
+                const dueCount = getDueCount(deck.id);
+                
+                return (
+                  <div
+                    key={deck.id}
+                    onClick={() =>
+                      router.push(`/memorize?deck_id=${deck.id}`)
+                    }
+                    className="flex flex-row items-center p-4 gap-3 hover:cursor-pointer hover:bg-gray-50 transition-colors border-b border-gray-100 last:border-b-0"
+                  >
+                    <div className="shrink-0">
+                      <Layers className="text-gray-600 w-5 h-5" />
+                    </div>
+                    <div className="flex-1">
+                      <div className="font-medium text-gray-900">
+                        {deck.name}
+                      </div>
+                      <div className="text-sm text-gray-500">
+                        {formatCardStats(stats)}
+                      </div>
+                    </div>
+                    {dueCount > 0 && (
+                      <div className="bg-blue-500 text-white text-xs font-bold px-2 py-1 rounded-full">
+                        {dueCount}
+                      </div>
+                    )}
+                    <div className="text-gray-400">
+                      <svg
+                        className="w-5 h-5"
+                        fill="none"
+                        stroke="currentColor"
+                        viewBox="0 0 24 24"
+                      >
+                        <path
+                          strokeLinecap="round"
+                          strokeLinejoin="round"
+                          strokeWidth={2}
+                          d="M9 5l7 7-7 7"
+                        />
+                      </svg>
+                    </div>
+                  </div>
+                );
+              })}
+          </div>
+        </>
+      )}
+    </PageLayout>
+  );
+};
+
+export { DeckSelector };