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

Move process wiring, technical adapters, and cross-cutting contracts out of flat internal/ packages so new code has a clear home without changing business layout.

internal/shared/constants.go

@@ -0,0 +1,6 @@
+// Copyright 2025 linux.do
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package shared 提供跨模块共享的常量、错误定义和通用类型。
+package shared