feat: add billing and usage domain cores

tests/usage-go-core-contract.test.ts

@@ -0,0 +1,14 @@
+import { readFile } from "node:fs/promises";
+import { describe, expect, it } from "vitest";
+
+describe("Go usage core compatibility fixture", () => {
+  it("freezes Shanghai boundaries, exclusions, dedupe, scope, and redaction", async () => {
+    const fixture = JSON.parse(await readFile("contracts/usage/core-v1.json", "utf8"));
+    expect(fixture).toEqual({
+      version: 1, timeZone: "Asia/Shanghai",
+      excluded: { sources: ["api"], providers: ["mock"] }, dedupeKey: "jobId",
+      scopes: { personal: "accountId", organization_admin: "organizationId", super_admin: "all" },
+      organizationAdminRedaction: ["accountUsername"]
+    });
+  });
+});