Relocate buildTypeEdges from construction.ts to type-compat.ts per architecture spec.
construction.ts re-exports it for backward compatibility. Add 10 unit tests for
buildTypeEdges covering compatible edges, incompatible edges with mismatches,
unknown schema passthrough, incremental construction, and edge deduplication.
Implements the core FlowGraph class with generic type parameters, DAG-enforced mutations,
cycle detection via graphology-dag, node/edge CRUD, traversal methods, and static factory stubs.