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/openflare/origin/errs.go

@@ -0,0 +1,13 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package origin
+
+const (
+	errOriginAddressRequired  = "源站地址不能为空"
+	errOriginAddressInvalid   = "源站地址格式不合法"
+	errOriginAddressExists    = "源站地址已存在"
+	errOriginDeleteReferenced = "该源站仍被规则引用，无法删除"
+	errOriginMissingPort      = "源站地址缺少端口"
+	errOriginNotFound         = "源站不存在"
+)