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/tls/errs.go

@@ -0,0 +1,26 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package tls
+
+const (
+	errCertificateNameRequired      = "certificate name cannot be empty"
+	errCertificateNameExists        = "certificate name already exists"
+	errCertificateContentRequired   = "certificate content and key content cannot be empty"
+	errCertificateContentInvalid    = "certificate or key format is invalid"
+	errCertificateDeleteReferenced  = "certificate is still referenced by proxy routes"
+	errCertificateOnlyACME          = "only acme certificates can be updated via this endpoint"
+	errCertificateOnlyUploadConvert = "only uploaded certificates can be converted to acme"
+	errCertificateAlreadyApplying   = "certificate is already applying"
+	errCertificateOnlyACMERenew     = "only acme certificates can be renewed"
+	errCertificateFilesRequired     = "certificate file and key file cannot be empty"
+	errCertificatePEMInvalid        = "证书 PEM 内容不合法"
+
+	errManagedDomainRequired        = "域名不能为空"
+	errManagedDomainInvalid         = "域名格式不合法"
+	errManagedDomainWildcardInvalid = "通配符域名仅支持 *.example.com 格式"
+	errManagedDomainExists          = "域名已存在"
+	errManagedDomainCertNotFound    = "所选证书不存在"
+
+	errDNSAccountInUse = "该 DNS 账号已被证书使用，无法删除"
+)