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.

pkg/util/strings.go

@@ -0,0 +1,35 @@
+// Copyright 2025 linux.do
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package util
+
+import "strings"
+
+// emailPartsCount 邮箱地址由 @ 分割为两部分
+const (
+	emailPartsCount    = 2
+	emailLocalMinChars = 2 // 邮箱 local 部分掩码显示的最小字符数
+)
+
+// DerefString 安全地解引用字符串指针，nil 返回空字符串
+func DerefString(s *string) string {
+	if s == nil {
+		return ""
+	}
+	return *s
+}
+
+// MaskEmail 安全脱敏用户的邮箱地址（例如 us***@example.com）
+func MaskEmail(email string) string {
+	parts := strings.Split(email, "@")
+	if len(parts) != emailPartsCount {
+		return email
+	}
+	local := parts[0]
+	domain := parts[1]
+	if len(local) <= emailLocalMinChars {
+		return "**@" + domain
+	}
+	return local[:2] + "***" + local[len(local)-1:] + "@" + domain
+}