Add memory coach, transformer recall model, and training FAB.

Introduce Q/K/V memory dialogue with coach APIs, a lightweight NumPy
transformer for per-word forgetting prediction, and a floating training
menu linking daily quiz, spell, and coach flows.

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

backend/main.py

@@ -3,7 +3,14 @@ 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
+from routers import (
+    auth_router,
+    coach_router,
+    quiz_router,
+    settings_router,
+    translate_router,
+    word_router,
+)
 
 Base.metadata.create_all(bind=engine)
 run_migrations()
@@ -23,6 +30,7 @@ app.include_router(translate_router.router)
 app.include_router(word_router.router)
 app.include_router(quiz_router.router)
 app.include_router(settings_router.router)
+app.include_router(coach_router.router)
 
 
 @app.get("/")