Replace types.ts standalone schemas with Metagraph Module re-exports

Delete types.ts and move all schema definitions to modules/metagraph.ts.
Named exports (GraphConfig, BaseNodeAttributes, BaseEdgeAttributes) use
Metagraph.Import() for -based references. Remove NodeType, EdgeType,
GraphSchema, GRAPH_BASE_TYPE, GraphBaseType (replaced by Module approach).
Update sqlite host imports to resolve from metagraph.ts.

src/graphs/mod.ts

@@ -1,6 +1,8 @@
-export * from "./types.ts";
 export {
   Metagraph,
+  GraphConfig,
+  BaseNodeAttributes,
+  BaseEdgeAttributes,
   GRAPH_STATUS,
   GraphStatus,
 } from "./modules/metagraph.ts";