fix(gateway): allow the native WebView origin via CORS

The packaged native app (Capacitor) serves the bundled SPA from a localhost scheme, so its Connect calls to erudit-game.ru are cross-origin. The gateway had no CORS handling, so the preflight OPTIONS returned 405 with no Access-Control-Allow-Origin and the WebView blocked every RPC — a native build could never reach the gateway and stayed stuck offline (the native online path was never exercised on-device; on-device D was airplane-mode only). Add a CORS middleware that answers the preflight and sets the response headers for the native localhost origins (https/http/capacitor://localhost); web is same-origin and untouched. Fixes the native emulator 'starts offline, can't go online' report.

gateway/internal/connectsrv/server.go

@@ -302,7 +302,7 @@ func (s *Server) HTTPHandler() http.Handler {
 	// honeypot hit is turned away before the body cap and the mux. Every request
 	// body on the public listener is then capped (the admin proxy POSTs included);
 	// the h2c server carries explicit stream/idle sizing.
-	return h2c.NewHandler(s.abuseGuard(maxBodyHandler(s.maxBodyBytes, mux)), &http2.Server{
+	return h2c.NewHandler(s.abuseGuard(withNativeCORS(maxBodyHandler(s.maxBodyBytes, mux))), &http2.Server{
 		MaxConcurrentStreams: h2cMaxConcurrentStreams,
 		IdleTimeout:          h2cIdleTimeout,
 	})