Create Metagraph Type.Module with Config, BaseNode, BaseEdge entries

Add src/graphs/modules/metagraph.ts exporting Metagraph as Type.Module()
with Config (Union defaults for type, Boolean defaults for multi/allowSelfLoops),
BaseNode (optional created/modified/metadata with Type.Unknown()), and
BaseEdge (type string, optional metadata with Type.Unknown()). Also export
GRAPH_STATUS const and GraphStatus TypeBox schema for sqlite host usage.
Update mod.ts to re-export from modules/metagraph.ts.

src/graphs/mod.ts

@@ -1,2 +1,7 @@
 export * from "./types.ts";
 export * from "./schemaBuilder.ts";
+export {
+  Metagraph,
+  GRAPH_STATUS,
+  GraphStatus,
+} from "./modules/metagraph.ts";