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/mtproto/process.go

@@ -1,7 +1,8 @@
-// Package mtproto manages mtg (github.com/9seconds/mtg) sidecar processes that
-// serve MTProto FakeTLS proxies. Xray-core has no mtproto protocol, so mtproto
-// inbounds are run as standalone mtg processes — one process per inbound —
-// entirely outside the Xray config and lifecycle.
+// Package mtproto manages mtg-multi (github.com/dolonet/mtg-multi) sidecar
+// processes that serve MTProto FakeTLS proxies. Xray-core has no mtproto
+// protocol, so mtproto inbounds are run as standalone mtg processes — one
+// process per inbound, each serving every active client's secret through the
+// mtg-multi [secrets] section — entirely outside the Xray config and lifecycle.
 package mtproto
 
 import (