feat(mtproto): add domain-fronting and essential mtg options

Expose mtg's [domain-fronting] section (ip/port/proxy-protocol) plus
proxy-protocol-listener, prefer-ip, and debug on MTProto inbounds. Each
key is written to the generated mtg-<id>.toml only when set, so mtg's own
defaults apply otherwise. The instance fingerprint now covers these
fields, so editing an option restarts the sidecar.

Since MTProto is mtg-served (not Xray), sniffing does not apply: hide the
Sniffing tab and the Advanced sniffing sub-editor, drop it from the
Advanced "All" JSON view, and emit empty sniffing in the wire payload,
all gated by a new canEnableSniffing predicate.

web/translation/es-ES.json

@@ -503,7 +503,13 @@
         "encryptionMethod": "Método de cifrado",
         "fakeTlsDomain": "Dominio FakeTLS (SNI)",
         "mtprotoSecret": "Secreto",
-        "mtprotoHint": "MTProto se sirve mediante un proceso mtg independiente, no Xray. Los ajustes de transporte y los clientes no aplican aquí; comparte el enlace de abajo con Telegram.",
+        "mtgDomainFrontingIp": "IP de domain fronting",
+        "mtgDomainFrontingPort": "Puerto de domain fronting",
+        "mtgDomainFrontingProxyProtocol": "Protocolo PROXY de domain fronting",
+        "mtgDomainFrontingHint": "Adónde envía mtg el tráfico que no es de Telegram, p. ej. tu sitio web falso de NGINX. Deja la IP vacía para usar el dominio FakeTLS mediante DNS; el puerto predeterminado es 443.",
+        "mtgProxyProtocolListener": "Aceptar protocolo PROXY (escucha)",
+        "mtgPreferIp": "Preferencia de IP",
+        "mtgDebug": "Registro de depuración",
         "visionTestseed": "Vision testseed",
         "version": "Versión",
         "udpIdleTimeout": "UDP idle timeout (s)",