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/service/client_inbound_apply.go

@@ -384,6 +384,10 @@ func (s *ClientService) addInboundClient(inboundSvc *InboundService, data *model
 			if client.PublicKey == "" {
 				return false, common.NewError("wireguard client requires a key")
 			}
+		case "mtproto":
+			if client.Secret == "" {
+				return false, common.NewError("mtproto client requires a secret")
+			}
 		default:
 			if client.ID == "" {
 				return false, common.NewError("empty client ID")
@@ -549,6 +553,8 @@ func (s *ClientService) UpdateInboundClient(inboundSvc *InboundService, data *mo
 		newClientId = clients[0].Auth
 	case "wireguard":
 		newClientId = clients[0].Email
+	case "mtproto":
+		newClientId = clients[0].Email
 	default:
 		newClientId = clients[0].ID
 	}