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.

frontend/src/test/__snapshots__/protocols.test.ts.snap

@@ -63,8 +63,21 @@ exports[`InboundSettingsSchema fixtures > parses mtproto-basic byte-stably 1`] =
 {
   "protocol": "mtproto",
   "settings": {
+    "clients": [
+      {
+        "comment": "",
+        "email": "mtproto-user",
+        "enable": true,
+        "expiryTime": 0,
+        "limitIp": 0,
+        "reset": 0,
+        "secret": "ee0123456789abcdef0123456789abcdef7777772e636c6f7564666c6172652e636f6d",
+        "subId": "",
+        "tgId": 0,
+        "totalGB": 0,
+      },
+    ],
     "fakeTlsDomain": "www.cloudflare.com",
-    "secret": "ee0123456789abcdef0123456789abcdef7777772e636c6f7564666c6172652e636f6d",
   },
 }
 `;
@@ -73,6 +86,20 @@ exports[`InboundSettingsSchema fixtures > parses mtproto-domain-fronting byte-st
 {
   "protocol": "mtproto",
   "settings": {
+    "clients": [
+      {
+        "comment": "",
+        "email": "mtproto-user",
+        "enable": true,
+        "expiryTime": 0,
+        "limitIp": 0,
+        "reset": 0,
+        "secret": "ee0123456789abcdef0123456789abcdef7777772e636c6f7564666c6172652e636f6d",
+        "subId": "",
+        "tgId": 0,
+        "totalGB": 0,
+      },
+    ],
     "debug": true,
     "domainFronting": {
       "ip": "127.0.0.1",
@@ -82,7 +109,7 @@ exports[`InboundSettingsSchema fixtures > parses mtproto-domain-fronting byte-st
     "fakeTlsDomain": "www.cloudflare.com",
     "preferIp": "prefer-ipv4",
     "proxyProtocolListener": true,
-    "secret": "ee0123456789abcdef0123456789abcdef7777772e636c6f7564666c6172652e636f6d",
+    "throttleMaxConnections": 5000,
   },
 }
 `;