Create new graph

Full graph model representing an existing graph from the database.

This is the primary model for working with persisted graphs. Includes all graph data (nodes, links, sub_graphs) plus user ownership and timestamps. Provides computed fields (input_schema, output_schema, etc.) used during set-up (frontend) and execution (backend).

Inherits from:

• Graph: provides structure (nodes, links, sub_graphs) and computed schemas
• GraphMeta: provides user_id, created_at for database records