Add reference data models and seed data for incoterms, invoice types, material types, payment methods, pedimento codes, pedimento regimens, sectors, states, transport modes, transport types, and valuation methods

- Implemented SQLAlchemy models for incoterms, invoice types, material types, payment methods, pedimento codes, pedimento regimens, sectors, states, transport modes, transport types, and valuation methods.
- Added seed data for each reference data model to populate the database with initial values.
- Ensured primary key constraints and appropriate data types for each model.
- Established relationships where necessary, particularly in pedimento codes and regimens.

backend/main.py

@@ -24,30 +24,11 @@ logging.basicConfig(
 
 logger = logging.getLogger(__name__)
 
-
-@asynccontextmanager
-async def lifespan(app: FastAPI):
-    """Lifecycle events"""
-    # Startup
-    logger.info("Starting Anexo76 API...")
-    try:
-        init_db()
-        logger.info("Database initialized successfully")
-    except Exception as e:
-        logger.error(f"Error initializing database: {str(e)}")
-    
-    yield
-    
-    # Shutdown
-    logger.info("Shutting down Anexo76 API...")
-
-
 # Crear aplicación FastAPI
 app = FastAPI(
     title="Anexo76 API",
     version=settings.APP_VERSION,
     description="Aplicación SaaS para gestión de comercio exterior conforme a Anexos 24, 31 y 22 del SAT",
-    lifespan=lifespan,
     docs_url="/docs" if settings.DEBUG else None,
     redoc_url="/redoc" if settings.DEBUG else None
 )