feat(contracts): openapi base, error codes, type generation

Co-Authored-By: Claude Code <noreply@anthropic.com>

packages/contracts/src/__tests__/errors.test.ts

@@ -0,0 +1,15 @@
+// 占位冒烟测试：仅验证 jest + ts-jest 工具链可用（Task 6 落地真正的类型测试）。
+import { ErrorCodes, type ErrorCode } from '../errors.js';
+
+describe('ErrorCodes', () => {
+  it('每个 key 映射到同名的稳定 code 字符串', () => {
+    for (const [key, code] of Object.entries(ErrorCodes)) {
+      expect(key).toBe(code);
+    }
+  });
+
+  it('ErrorCode 联合类型可收窄具体 code', () => {
+    const code: ErrorCode = ErrorCodes.ALBUM_NOT_FOUND;
+    expect(code).toBe('ALBUM_NOT_FOUND');
+  });
+});