feat: add public status page with component health monitoring and system metrics visualization

Add statuspage package with service, handler, and types for exposing platform health. Implement GET /api/v1/status endpoint returning operational status, component health (API, database, gateway runtime), and control plane summary counts.

Add Service.Snapshot method querying database connectivity, user/device/gateway/service/policy counts, connected device count via handshake timestamps, and gateway runtime tel

backend/internal/httpserver/router.go

@@ -13,6 +13,7 @@ import (
 	"nexavpn/backend/internal/group"
 	"nexavpn/backend/internal/policy"
 	"nexavpn/backend/internal/servicecatalog"
+	"nexavpn/backend/internal/statuspage"
 	"nexavpn/backend/internal/user"
 )
 
@@ -25,6 +26,7 @@ type Handlers struct {
 	Gateway *gateway.Handler
 	Group   *group.Handler
 	Audit   *audit.Handler
+	Status  *statuspage.Handler
 }
 
 func NewRouter(jwtSecret string, handlers Handlers) http.Handler {
@@ -36,6 +38,7 @@ func NewRouter(jwtSecret string, handlers Handlers) http.Handler {
 	})
 
 	r.Route("/api/v1", func(r chi.Router) {
+		r.Get("/status", handlers.Status.PublicStatus)
 		r.Get("/auth/bootstrap/status", handlers.Auth.BootstrapStatus)
 		r.Post("/auth/bootstrap", handlers.Auth.Bootstrap)
 		r.Post("/auth/login", handlers.Auth.Login)