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/zh-CN.json

@@ -542,6 +542,9 @@
         "mtgRouteOutbound": "出站",
         "mtgRouteOutboundHint": "可选。强制 Telegram 流量经由此出站（或负载均衡器）发出。留空则由您的路由规则决定。",
         "mtgRouteOutboundPlaceholder": "使用路由规则",
+        "mtprotoFakeTlsDomainHint": "生成新客户端密钥时使用的默认 FakeTLS 域名。每个客户端可使用各自的域名。",
+        "mtgThrottleMaxConnections": "最大连接数",
+        "mtgThrottleMaxConnectionsHint": "按公平分配限制所有用户的并发连接数。0 表示不限制。",
         "visionTestseed": "Vision testseed",
         "version": "版本",
         "udpIdleTimeout": "UDP 空闲超时 (s)",
@@ -907,6 +910,8 @@
       "wireguardPreSharedKey": "WireGuard 预共享密钥",
       "wireguardAllowedIPs": "WireGuard 允许的 IP",
       "wireguardAllowedIPsHint": "留空则自动分配；多个条目用逗号分隔",
+      "mtprotoSecret": "MTProto 密钥",
+      "mtprotoSecretHint": "该客户端的 FakeTLS 密钥。重新生成即可更换。",
       "reverseTag": "反向标签",
       "reverseTagPlaceholder": "可选 Reverse tag",
       "telegramId": "Telegram 用户 ID",