Expose /metrics endpoint on admin socket via promhttp

internal/app/admin.go

@@ -31,6 +31,7 @@ import (
 	"time"
 
 	"github.com/gin-gonic/gin"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 
 	admin "git.happydns.org/happyDomain/internal/api-admin/route"
 	providerUC "git.happydns.org/happyDomain/internal/usecase/provider"
@@ -56,6 +57,8 @@ func NewAdmin(app *App) *Admin {
 	// Prepare usecases (admin uses unrestricted provider access)
 	app.usecases.providerAdmin = providerUC.NewService(app.store, nil)
 
+	router.GET("/metrics", gin.WrapH(promhttp.Handler()))
+
 	admin.DeclareRoutes(
 		app.cfg,
 		router,