feat: add module schema discovery and validation

tests/fixtures/boundaries/module-schema-imports-module/modules/calendar/src/schema.ts

@@ -0,0 +1,3 @@
+import { peopleRecords } from "../../../modules/people/src/schema.js";
+
+export const invalidPrivateSchemaImport = peopleRecords;

tests/fixtures/boundaries/module-schema-imports-module/modules/people/src/schema.ts

@@ -0,0 +1 @@
+export const peopleRecords = "private people schema";