feat(mtproto): adopt dolonet/mtg-multi and make MTProto inbounds multi-client

Replace the upstream 9seconds/mtg sidecar with the dolonet/mtg-multi fork so a single MTProto inbound can serve many per-user secrets. Each panel client is now one named FakeTLS secret in the fork's [secrets] section: clients are first-class (attach/detach, limits, expiry, per-client tg:// links) exactly like every other protocol, mirroring the WireGuard multi-client model. Per-client traffic and online status come from the fork's /stats JSON API (its Prometheus output has no per-user label), fed into the existing email-keyed client_traffics accumulator; an optional throttle caps concurrent connections. A one-time seeder converts each legacy single-secret inbound into a one-client inbound.

The fork ships only linux/darwin amd64/arm64 binaries but is pure Go, so provisioning builds it from source for every supported platform (release.yml, DockerInit.sh) while keeping the panel-expected mtg-<os>-<arch> filename and the 'run' verb, so process.go is untouched. Also fixes a pre-existing update.sh gap that never renamed the mtg binary for armv6/armv7 updates.

internal/web/translation/es-ES.json

@@ -522,6 +522,9 @@
         "mtgRouteOutbound": "Salida",
         "mtgRouteOutboundHint": "Opcional. Fuerza el tráfico de Telegram a salir por esta salida (o balanceador). Déjalo vacío para que decidan tus reglas de enrutamiento.",
         "mtgRouteOutboundPlaceholder": "Usar reglas de enrutamiento",
+        "mtprotoFakeTlsDomainHint": "Dominio FakeTLS predeterminado para generar el secreto de un nuevo cliente. Cada cliente puede usar su propio dominio.",
+        "mtgThrottleMaxConnections": "Conexiones máximas",
+        "mtgThrottleMaxConnectionsHint": "Limita las conexiones simultáneas de todos los usuarios con reparto equitativo. 0 desactiva el límite.",
         "visionTestseed": "Vision testseed",
         "version": "Versión",
         "udpIdleTimeout": "UDP idle timeout (s)",
@@ -907,6 +910,8 @@
       "wireguardPreSharedKey": "Clave precompartida de WireGuard",
       "wireguardAllowedIPs": "IP permitidas de WireGuard",
       "wireguardAllowedIPsHint": "Déjalo vacío para asignar automáticamente; separa las entradas con comas",
+      "mtprotoSecret": "Secreto MTProto",
+      "mtprotoSecretHint": "El secreto FakeTLS del cliente. Vuelve a generarlo para cambiarlo.",
       "reverseTag": "Etiqueta inversa",
       "reverseTagPlaceholder": "Reverse tag opcional",
       "telegramId": "ID de usuario de Telegram",