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/node/errs.go

@@ -0,0 +1,21 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package node
+
+const (
+	errNodeNameRequired          = "节点名不能为空"
+	errNodeIPTooLong             = "节点 IP 不能超过 64 个字符"
+	errNodeIPInvalid             = "节点 IP 格式无效"
+	errNodeIPManualRequired      = "锁定节点 IP 时必须填写节点 IP"
+	errNodeGeoNameTooLong        = "节点位置名不能超过 128 个字符"
+	errNodeGeoCoordinateMismatch = "地图坐标必须同时填写纬度和经度"
+	errNodeGeoLatitudeInvalid    = "纬度必须在 -90 到 90 之间"
+	errNodeGeoLongitudeInvalid   = "经度必须在 -180 到 180 之间"
+	errNodeIDConflict            = "节点标识生成冲突，请重试"
+	errNodeNotFound              = "节点不存在"
+	errNodeForceSyncFailed       = "节点不在线或通过 WebSocket 发送同步指令失败"
+	errNoActiveConfigVersion     = "当前没有激活版本"
+	errAgentPreviewTagInvalid    = "指定版本不是 preview 发布"
+	errAgentStableTagInvalid     = "正式版更新不能选择 preview 发布"
+)