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/user/constants.go

@@ -0,0 +1,15 @@
+// Copyright 2025 linux.do
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package user
+
+import "time"
+
+const (
+	verificationCodeRange  = 900000           // 验证码随机范围
+	verificationCodeOffset = 100000           // 验证码偏移量（保证 6 位）
+	emailCodeExpiry        = 5 * time.Minute  // 验证码有效期
+	emailCodeCooldown      = 60 * time.Second // 验证码发送冷却时间
+	minPasswordLength      = 8                // 密码最小长度
+)