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/updater/errs.go

@@ -0,0 +1,17 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package updater manages GitHub Release checks and in-place application upgrades.
+package updater
+
+const (
+	errInvalidRepository       = "上游仓库地址无效"
+	errReleaseRequestFailed    = "获取上游版本失败"
+	errReleaseResponseInvalid  = "上游版本响应无效"
+	errNoCompatibleRelease     = "未找到兼容的 Release"
+	errNoCompatibleAsset       = "未找到当前系统对应的 Release 资产"
+	errDevelopmentBuild        = "开发版本无法执行自动升级"
+	errAlreadyUpToDate         = "当前已是最新版本"
+	errUpgradeAlreadyRunning   = "已有升级任务正在执行"
+	errAutomaticUpgradeBlocked = "当前平台暂不支持自动替换二进制"
+)