refactor(structure): group platform, infra, and shared packages

Reorganize internal packages into platform/infra/shared layers and update
imports, docs, and seed-count tests to match current system configs.

frontend/lib/api-envelope.ts

@@ -1,6 +1,6 @@
 /**
  * OpenFlare 统一 API 响应信封解析。
- * 与后端 internal/common/response.Response 及 axios api-client 约定一致。
+ * 与后端 internal/shared/response.Response 及 axios api-client 约定一致。
  */
 
 export interface ApiEnvelope<T = unknown> {