Add spell practice, memory analytics, auth persistence, and word library UX.

Includes per-word training stats and curves, quiz session auto-save, remember-login,
paginated word list with floating page arrows, and Obsidian-style relationship graph baseline.

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

backend/services/quiz_service.py

@@ -118,6 +118,27 @@ class QuizService:
             correct_answer=correct,
         )
 
+    def build_spell_question(self, word: Word) -> QuizQuestion:
+        zh = word.source_text if word.source_lang == "zh" else word.target_text
+        en = word.target_text if word.source_lang == "zh" else word.source_text
+        return QuizQuestion(
+            word_id=word.id,
+            question_type="spell",
+            prompt=zh,
+            phonetic=word.phonetic,
+            options=[],
+            correct_answer=en,
+        )
+
+    def get_spell_quiz(self, db: Session, user: User) -> dict:
+        settings = self.get_settings(db, user)
+        words = self.select_daily_words(db, user, settings.daily_target)
+        questions = [self.build_spell_question(w) for w in words]
+        return {
+            "questions": questions,
+            "total": len(questions),
+        }
+
     def get_daily_quiz(self, db: Session, user: User) -> dict:
         settings = self.get_settings(db, user)
         words = self.select_daily_words(db, user, settings.daily_target)
@@ -143,6 +164,7 @@ class QuizService:
         question_type: str,
         user_answer: str,
         correct_answer: str,
+        duration_seconds: int = 0,
     ) -> dict:
         word = db.query(Word).filter(Word.id == word_id, Word.user_id == user.id).first()
         if not word:
@@ -150,9 +172,15 @@ class QuizService:
             raise HTTPException(status_code=404, detail="单词不存在")
 
         settings = self.get_settings(db, user)
-        is_correct = user_answer.strip() == correct_answer.strip()
+        if question_type == "spell":
+            is_correct = (
+                user_answer.strip().lower() == correct_answer.strip().lower()
+            )
+        else:
+            is_correct = user_answer.strip() == correct_answer.strip()
         now = utc_now_iso()
         today = today_str()
+        duration_seconds = max(0, min(int(duration_seconds or 0), 3600))
 
         if is_correct:
             word.correct_count += 1
@@ -175,6 +203,8 @@ class QuizService:
 
         word.mastery_score = calc_mastery_score(word.correct_count, word.wrong_count)
         word.last_reviewed_at = now
+        word.train_count += 1
+        word.total_train_seconds += duration_seconds
 
         record = QuizRecord(
             user_id=user.id,
@@ -183,6 +213,7 @@ class QuizService:
             user_answer=user_answer,
             correct_answer=correct_answer,
             is_correct=1 if is_correct else 0,
+            duration_seconds=duration_seconds,
             created_at=now,
         )
         db.add(record)