feat: 添加 Anki APKG 导入/导出功能

- 添加 APKG 解析器 (src/lib/anki/apkg-parser.ts)
- 添加 APKG 导出器 (src/lib/anki/apkg-exporter.ts)
- 添加导入/导出 Server Actions
- 添加导入/导出 UI 组件
- 集成到牌组页面
- 添加 i18n 翻译

同时修复断链:
- /folders → /decks (Navbar, signup, profile)

src/lib/anki/apkg-parser.ts

@@ -0,0 +1,174 @@
+import JSZip from "jszip";
+import initSqlJs from "sql.js";
+import type { Database, SqlValue } from "sql.js";
+import {
+  type AnkiDeck,
+  type AnkiNoteType,
+  type AnkiDeckConfig,
+  type AnkiNoteRow,
+  type AnkiCardRow,
+  type AnkiRevlogRow,
+  type ParsedApkg,
+} from "./types";
+
+async function openDatabase(zip: JSZip): Promise<Database | null> {
+  const SQL = await initSqlJs({
+    locateFile: (file: string) => `https://sql.js.org/dist/${file}`,
+  });
+  
+  const anki21b = zip.file("collection.anki21b");
+  const anki21 = zip.file("collection.anki21");
+  const anki2 = zip.file("collection.anki2");
+  
+  let dbFile = anki21b || anki21 || anki2;
+  if (!dbFile) return null;
+  
+  const dbData = await dbFile.async("uint8array");
+  return new SQL.Database(dbData);
+}
+
+function parseJsonField<T>(jsonStr: string): T {
+  try {
+    return JSON.parse(jsonStr);
+  } catch {
+    return {} as T;
+  }
+}
+
+function queryAll<T>(db: Database, sql: string, params: SqlValue[] = []): T[] {
+  const results: T[] = [];
+  const stmt = db.prepare(sql);
+  stmt.bind(params);
+  
+  while (stmt.step()) {
+    const row = stmt.getAsObject();
+    results.push(row as T);
+  }
+  
+  stmt.free();
+  return results;
+}
+
+function queryOne<T>(db: Database, sql: string, params: SqlValue[] = []): T | null {
+  const results = queryAll<T>(db, sql, params);
+  return results[0] ?? null;
+}
+
+export async function parseApkg(buffer: Buffer): Promise<ParsedApkg> {
+  const zip = await JSZip.loadAsync(buffer);
+  const db = await openDatabase(zip);
+  
+  if (!db) {
+    throw new Error("No valid Anki database found in APKG file");
+  }
+  
+  const col = queryOne<{ 
+    crt: number; 
+    mod: number; 
+    ver: number;
+    conf: string;
+    models: string;
+    decks: string;
+    dconf: string;
+    tags: string;
+  }>(db, "SELECT crt, mod, ver, conf, models, decks, dconf, tags FROM col WHERE id = 1");
+  
+  if (!col) {
+    db.close();
+    throw new Error("Invalid APKG: no collection row found");
+  }
+  
+  const decksMap = new Map<number, AnkiDeck>();
+  const decksJson = parseJsonField<Record<string, AnkiDeck>>(col.decks);
+  for (const [id, deck] of Object.entries(decksJson)) {
+    decksMap.set(parseInt(id, 10), deck);
+  }
+  
+  const noteTypesMap = new Map<number, AnkiNoteType>();
+  const modelsJson = parseJsonField<Record<string, AnkiNoteType>>(col.models);
+  for (const [id, model] of Object.entries(modelsJson)) {
+    noteTypesMap.set(parseInt(id, 10), model);
+  }
+  
+  const deckConfigsMap = new Map<number, AnkiDeckConfig>();
+  const dconfJson = parseJsonField<Record<string, AnkiDeckConfig>>(col.dconf);
+  for (const [id, config] of Object.entries(dconfJson)) {
+    deckConfigsMap.set(parseInt(id, 10), config);
+  }
+  
+  const notes = queryAll<AnkiNoteRow>(
+    db, 
+    "SELECT id, guid, mid, mod, usn, tags, flds, sfld, csum, flags, data FROM notes"
+  );
+  
+  const cards = queryAll<AnkiCardRow>(
+    db,
+    "SELECT id, nid, did, ord, mod, usn, type, queue, due, ivl, factor, reps, lapses, left, odue, odid, flags, data FROM cards"
+  );
+  
+  const revlogs = queryAll<AnkiRevlogRow>(
+    db,
+    "SELECT id, cid, usn, ease, ivl, lastIvl, factor, time, type FROM revlog"
+  );
+  
+  const mediaMap = new Map<string, Buffer>();
+  const mediaFile = zip.file("media");
+  if (mediaFile) {
+    const mediaJson = parseJsonField<Record<string, string>>(await mediaFile.async("text"));
+    for (const [num, filename] of Object.entries(mediaJson)) {
+      const mediaData = zip.file(num);
+      if (mediaData) {
+        const data = await mediaData.async("nodebuffer");
+        mediaMap.set(filename, data);
+      }
+    }
+  }
+  
+  db.close();
+  
+  return {
+    decks: decksMap,
+    noteTypes: noteTypesMap,
+    deckConfigs: deckConfigsMap,
+    notes,
+    cards,
+    revlogs,
+    media: mediaMap,
+    collectionMeta: {
+      crt: col.crt,
+      mod: col.mod,
+      ver: col.ver,
+    },
+  };
+}
+
+export function getDeckNotesAndCards(
+  parsed: ParsedApkg,
+  deckId: number
+): { notes: AnkiNoteRow[]; cards: AnkiCardRow[] } {
+  const deckCards = parsed.cards.filter(c => c.did === deckId);
+  const noteIds = new Set(deckCards.map(c => c.nid));
+  const deckNotes = parsed.notes.filter(n => noteIds.has(n.id));
+  
+  return { notes: deckNotes, cards: deckCards };
+}
+
+export function getDeckNames(parsed: ParsedApkg): { id: number; name: string; cardCount: number }[] {
+  const cardCounts = new Map<number, number>();
+  for (const card of parsed.cards) {
+    cardCounts.set(card.did, (cardCounts.get(card.did) ?? 0) + 1);
+  }
+  
+  const result: { id: number; name: string; cardCount: number }[] = [];
+  for (const [id, deck] of parsed.decks) {
+    if (deck.dyn === 0) {
+      result.push({
+        id,
+        name: deck.name,
+        cardCount: cardCounts.get(id) ?? 0,
+      });
+    }
+  }
+  
+  return result.sort((a, b) => a.name.localeCompare(b.name));
+}