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/upload/shared/constants.go

@@ -0,0 +1,20 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package shared
+
+// Upload size, path, media quality, and cache constants shared across subpackages.
+const (
+	MaxUploadSize           = 32 * 1024 * 1024 // 32MB
+	DetectContentBytes      = 512              // http.DetectContentType 需要的最小字节数
+	UploadDirPerm           = 0755             // 上传目录权限
+	UploadFilePerm          = 0644             // 上传文件权限
+	ImageQualityLow         = "low"
+	ImageQualityMedium      = "medium"
+	ImageQualityHigh        = "high"
+	ImageQualityOrigin      = "origin"
+	DefaultPublicUploadType = "avatar"
+	FileStatsTrendDays      = 7
+	MaxS3KeyLength          = 1024
+	AccessCacheTTL          = 5 // seconds; multiplied by time.Second at use site
+)