feat: add user model and registration endpoint

backend/app/main.py

@@ -1,6 +1,21 @@
+from contextlib import asynccontextmanager
+
 from fastapi import FastAPI
 
-app = FastAPI(title="Quantumancy")
+import app.models  # noqa: F401 — registers models on Base.metadata before create_all
+from app.db import Base, engine
+from app.routes.auth import router as auth_router
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    yield
+
+
+app = FastAPI(title="Quantumancy", lifespan=lifespan)
+app.include_router(auth_router)
 
 
 @app.get("/healthz")