refactor(repo): consolidate openflare-server to root and move subprojects to internal/apps

- Merge all files inside openflare-server to the repository root directory.
- Relocate agent, relay, and flared subprojects from internal/ to internal/apps/.
- Combine docker-compose files and update build context paths to root.
- Update GitHub workflows and Dockerfiles to refer to new directories and package names.
- Rewrite Go package imports across all files.
- Resolve database renew test race condition and clean up docs.

internal/apps/admin/template/errs.go

@@ -0,0 +1,16 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package template 提供模板管理功能
+package template
+
+// 模板管理相关错误消息
+const (
+	TemplateNotFound              = "模板不存在"
+	TemplateKeyRequired           = "模板标识符不能为空"
+	TemplateNameRequired          = "模板名称不能为空"
+	TemplateContentRequired       = "模板内容不能为空"
+	TemplateKeyExists             = "模板标识符已存在"
+	SystemTemplateCannotDelete    = "系统预置模板不可删除"
+	SystemTemplateCannotModifyKey = "系统预置模板不可修改标识符"
+)