Add database auto-creation on startup

backend/app/main.py

@@ -1,19 +1,35 @@
 """BIM Twin Viewer — FastAPI application entry point."""
 
+from contextlib import asynccontextmanager
+
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.api import health, elements, upload
+from app.models.database import engine, Base
+
+# Import all models so Base.metadata knows about them
+from app.models import element  # noqa: F401
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Create database tables on startup."""
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    yield
+
 
 app = FastAPI(
     title="BIM Twin Viewer API",
     description="REST API for IFC-based 3D building model inspection",
     version="0.1.0",
+    lifespan=lifespan,
 )
 
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["*"],  # tighten in production
+    allow_origins=["*"],
     allow_credentials=True,
     allow_methods=["*"],
     allow_headers=["*"],