feat: Add welcome message for non-WebSocket GET requests

Instead of returning WebSocket upgrade error for plain GET requests,
now returns RelayInfo.Name (if set) or empty 200 OK.

Users who want custom messages can wrap Relay with their own ServeMux.

🌸 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Sakura 🌸 <noreply@anthropic.com>

Author: high-moctane

relay.go

@@ -114,13 +114,29 @@ func (r *Relay) unregisterConn(id uint64) {
 
 // ServeHTTP implements http.Handler.
 func (r *Relay) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	// Check if relay is shutting down (for all requests)
+	r.mu.Lock()
+	closed := r.closed
+	r.mu.Unlock()
+
+	if closed {
+		http.Error(w, "relay is shutting down", http.StatusServiceUnavailable)
+		return
+	}
+
 	// NIP-11: Respond with relay info if Accept header is application/nostr+json
 	if r.Info != nil && req.Header.Get("Accept") == "application/nostr+json" {
 		r.serveNIP11(w, req)
 		return
 	}
 
-	// Check if relay is shutting down and register connection atomically
+	// Non-WebSocket GET: return simple message instead of upgrade error
+	if req.Header.Get("Upgrade") == "" {
+		r.serveWelcome(w, req)
+		return
+	}
+
+	// WebSocket connection: track with WaitGroup
 	r.mu.Lock()
 	if r.closed {
 		r.mu.Unlock()
@@ -384,6 +400,18 @@ func (r *Relay) logWarn(ctx context.Context, msg string, args ...any) {
 	}
 }
 
+// serveWelcome responds with a simple welcome message for non-WebSocket requests.
+// If RelayInfo.Name is set, it returns the name. Otherwise, returns empty 200 OK.
+func (r *Relay) serveWelcome(w http.ResponseWriter, req *http.Request) {
+	if r.Info != nil && r.Info.Name != "" {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.Write([]byte(r.Info.Name))
+		return
+	}
+	// Empty 200 OK
+	w.WriteHeader(http.StatusOK)
+}
+
 // serveNIP11 responds with the NIP-11 Relay Information Document.
 func (r *Relay) serveNIP11(w http.ResponseWriter, req *http.Request) {
 	// CORS headers (required by NIP-11)