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/custom/routers.go

@@ -0,0 +1,24 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package custom provides custom business handlers
+package custom
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/Rain-kl/Wavelet/internal/common/response"
+)
+
+// Hello is a sample handler for custom business logic
+// @Summary Sample Hello API
+// @Description A sample business API for customization
+// @Tags custom
+// @Produce json
+// @Success 200 {object} response.Any{data=string} "成功"
+// @Router /api/v1/custom/hello [get]
+func Hello(c *gin.Context) {
+	c.JSON(http.StatusOK, response.OK("Hello from custom business module!"))
+}