refactor: serve metrics on main HTTP port instead of separate port

Move metrics dashboard and Prometheus endpoint to the main HTTP server
for simplified deployment and single ingress configuration.

Changes:
- Add PrometheusHandler() and DashboardHandler() methods to Metrics
- Serve /dashboard on main HTTP port (was root on separate port)
- Serve /metrics on main HTTP port (was /metrics on separate port)
- Remove separate metrics server goroutine
- Update logging to show metrics paths on main HTTP port

Benefits:
- Single port/ingress needed for all HTTP traffic
- Simpler reverse proxy configuration
- Dashboard accessible alongside main relay endpoints

Endpoints on port 8080:
- / - WebSocket/index
- /nostr.v1.NostrRelay/* - Connect (gRPC-Web)
- /dashboard - Metrics dashboard (HTML)
- /metrics - Prometheus metrics (text)

2 files changed, 18 insertions, 10 deletions

diff --git a/cmd/relay/main.go b/cmd/relay/main.go
index 209d758..bd50e63 100644
--- a/cmd/relay/main.go
+++ b/cmd/relay/main.go
@@ -85,12 +85,8 @@ func main() {
                         grpc.ChainStreamInterceptor(metrics.StreamServerInterceptor(m)),
                 )
 
-                go func() {
-                        log.Printf("Metrics server listening on %s%s", cfg.Metrics.Addr, cfg.Metrics.Path)
-                        if err := m.Serve(cfg.Metrics.Addr, cfg.Metrics.Path); err != nil {
-                                log.Printf("Metrics server failed: %v", err)
-                        }
-                }()
+                mux.Handle("/metrics", m.PrometheusHandler())
+                mux.Handle("/dashboard", m.DashboardHandler())
         }
 
         wsHandler := wshandler.NewHandler(store, subManager)
@@ -127,6 +123,10 @@ func main() {
         log.Printf("HTTP server listening on %s", cfg.Server.HttpAddr)
         log.Printf("  - Connect (gRPC-Web) at %s/nostr.v1.NostrRelay/*", cfg.Server.HttpAddr)
         log.Printf("  - WebSocket (Nostr) at %s/", cfg.Server.HttpAddr)
+        if cfg.Metrics.Enabled {
+                log.Printf("  - Metrics dashboard at %s/dashboard", cfg.Server.HttpAddr)
+                log.Printf("  - Prometheus metrics at %s/metrics", cfg.Server.HttpAddr)
+        }
         log.Printf("Database: %s", cfg.Database.Path)
         if cfg.Auth.Read.Enabled || cfg.Auth.Write.Enabled {
                 log.Printf("Auth: enabled (read=%v write=%v)", cfg.Auth.Read.Enabled, cfg.Auth.Write.Enabled)
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
index 9030775..74f9ffb 100644
--- a/internal/metrics/metrics.go
+++ b/internal/metrics/metrics.go
@@ -288,12 +288,20 @@ const (
 //go:embed dashboard.html
 var dashboardHTML []byte
 
-func (m *Metrics) Serve(addr, path string) error {
-        mux := http.NewServeMux()
-        mux.Handle(path, promhttp.Handler())
-        mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+func (m *Metrics) PrometheusHandler() http.Handler {
+        return promhttp.Handler()
+}
+
+func (m *Metrics) DashboardHandler() http.Handler {
+        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
                 w.Header().Set("Content-Type", "text/html; charset=utf-8")
                 w.Write(dashboardHTML)
         })
+}
+
+func (m *Metrics) Serve(addr, path string) error {
+        mux := http.NewServeMux()
+        mux.Handle(path, m.PrometheusHandler())
+        mux.Handle("/", m.DashboardHandler())
         return http.ListenAndServe(addr, mux)
 }