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/routers/word_router.py

@@ -6,7 +6,14 @@ from sqlalchemy.orm import Session
 from auth import get_current_user
 from database import get_db
 from models import User
-from schemas import WordCreate, WordOut, WordUpdate
+from schemas import (
+    MemoryVisualizationResponse,
+    WordCreate,
+    WordMemoryDetailResponse,
+    WordOut,
+    WordUpdate,
+)
+from services.memory_visual_service import memory_visual_service
 from services.word_service import word_service
 
 router = APIRouter(prefix="/api/words", tags=["words"])
@@ -31,6 +38,23 @@ def list_words(
     return word_service.list_words(db, current_user, status)
 
 
+@router.get("/memory-viz", response_model=MemoryVisualizationResponse)
+def memory_visualization(
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    return memory_visual_service.get_visualization(db, current_user)
+
+
+@router.get("/{word_id}/memory", response_model=WordMemoryDetailResponse)
+def word_memory(
+    word_id: int,
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    return memory_visual_service.get_word_memory(db, current_user, word_id)
+
+
 @router.get("/{word_id}", response_model=WordOut)
 def get_word(
     word_id: int,