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/main.py

@@ -2,9 +2,11 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from database import Base, engine
+from db_migrate import run_migrations
 from routers import auth_router, quiz_router, settings_router, translate_router, word_router
 
 Base.metadata.create_all(bind=engine)
+run_migrations()
 
 app = FastAPI(title="WordLoop API", version="1.0.0")