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/admin/push/constants.go

@@ -0,0 +1,15 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package push
+
+const (
+	channelCustom    = "custom"
+	channelEmail     = "email"
+	channelLark      = "lark"
+	channelTelegram  = "telegram"
+	defaultLevelInfo = "INFO"
+	keyTitle         = "title"
+	keyContent       = "content"
+	keyLevel         = "level"
+)